Quiz: Electromagnetic Waves and Optics — 61 questions

1. Regarding scalar quantities, which statements are correct?

A. Energy and power are examples of scalar quantities.

B. A scalar quantity requires both magnitude and direction for complete specification.

C. A scalar quantity is represented by an arrow with magnitude and direction.

D. Time and temperature are examples of scalar quantities.

E. A scalar quantity is specified by one number and an appropriate unit.

Answer: (A), (D), (E)

Explanation

A scalar is completely specified by a numerical value and a suitable unit, and time, temperature, energy, and power are scalar examples. Scalars do not require direction and are not defined by vector arrows.

2. Concerning vector quantities, select the correct statements:

A. Temperature and energy are examples of vector quantities.

B. Displacement and velocity are examples of vector quantities.

C. A vector quantity is specified by both magnitude and direction.

D. A vector quantity has magnitude but no directional information.

E. A vector quantity is completely specified by a single number and unit.

Answer: (B), (C)

Explanation

Vectors require both magnitude and direction, and displacement and velocity are vector examples. A single number describes a scalar, while temperature and energy are scalars; omitting direction does not fully specify a vector.

3. Regarding the graphical representation of a vector, which statements are correct?

A. The length of a vector arrow represents its magnitude when drawn to scale.

B. The arrowhead indicates the vector’s direction.

C. The arrowhead determines the vector’s magnitude in a scaled diagram.

D. A longer scaled arrow represents a vector with greater magnitude.

E. The arrow length indicates the vector’s direction.

Answer: (A), (B), (D)

Explanation

For a vector drawn to scale, arrow length represents magnitude and the arrowhead represents direction. Therefore, a longer scaled arrow indicates greater magnitude, whereas arrow length itself does not indicate direction.

4. When drawing a vector graphically, which statements are correct?

A. The arrow length can be selected without using a scale.

B. The scale determines the arrow’s orientation rather than its length.

C. The vector’s magnitude need not be labelled after drawing the arrow.

D. The arrow should be drawn in the required direction with an arrowhead.

E. A scale should be chosen and recorded before determining the arrow length.

Answer: (D), (E)

Explanation

Vector construction involves choosing and recording a scale, calculating the arrow length from it, drawing the required direction with an arrowhead, and labelling the magnitude. Thus, scale is used for length, not orientation, and the magnitude should be labelled.

5. For two vectors $\mathbf{A}$ and $\mathbf{B}$, which statement correctly describes their resultant?

A. Their resultant is expressed as $\mathbf{R}=\mathbf{A}\times\mathbf{B}$.

B. Their resultant is expressed as $\mathbf{R}=\mathbf{A}+\mathbf{B}$.

C. Their resultant is expressed as $\mathbf{R}=\mathbf{A}+(-\mathbf{B})$.

D. Their resultant is expressed as $\mathbf{R}=\mathbf{A}-\mathbf{B}$.

E. Their resultant is expressed as $\mathbf{R}=\mathbf{A}/\mathbf{B}$.

Answer: (B)

Explanation

The resultant of vectors $\mathbf{A}$ and $\mathbf{B}$ is their vector sum, $\mathbf{R}=\mathbf{A}+\mathbf{B}$. Subtracting $\mathbf{B}$ would instead produce $\mathbf{A}-\mathbf{B}$, while multiplication and division are not the stated resultant operation.

6. Vector resolution refers to which of the following statements?

A. It changes a vector into a scalar by removing its direction.

B. It represents a vector using component vectors.

C. It breaks a vector into component vectors whose sum equals the original vector.

D. It produces components that together reproduce the original vector.

E. It combines vectors into a single vector with the same overall effect.

Answer: (B), (C), (D)

Explanation

Vector resolution breaks one vector into components whose vector sum equals the original. Combining vectors into one equivalent vector describes a resultant, while resolution does not convert a vector into a scalar.

7. Concerning the position of an object, which statements are correct?

A. Position is the total length of the path traveled by an object.

B. Position identifies location relative to a chosen reference origin.

C. Position is a scalar quantity describing path length.

D. Position specifies an object’s location relative to an origin or reference frame.

E. Position may have a positive or negative value.

Answer: (B), (D), (E)

Explanation

Position gives an object’s location relative to an origin or reference frame and may be positive or negative. Total path length is distance, and describing position as path length or a scalar path measure confuses it with distance.

8. Distance and displacement differ in which ways?

A. Distance is the final position, whereas displacement is the initial position.

B. Distance is total path length, whereas displacement is the change from initial to final position.

C. Distance measures the straight-line change, whereas displacement measures total path length.

D. Distance is a vector, whereas displacement is a scalar.

E. Distance and displacement both describe total path length as scalars.

Answer: (B)

Explanation

Distance is the total length of the path and is scalar, whereas displacement is the difference between final and initial positions and is vectorial. The other statements interchange these definitions or confuse them with position.

9. For an object moving from position $s_0$ at time $t_0$ to position $s$ at time $t$, which statements are correct?

A. Average velocity is calculated as $\frac{s_0-s}{t-t_0}$.

B. Average velocity is displacement divided by the corresponding time interval.

C. Average velocity is calculated as $\frac{s-s_0}{t+t_0}$.

D. Average velocity is calculated as $\frac{s+s_0}{t-t_0}$.

E. Average velocity is calculated as $\frac{\Delta s}{\Delta t}$.

Answer: (B), (E)

Explanation

Average velocity equals displacement divided by elapsed time, so $v_{av}=\frac{\Delta s}{\Delta t}=\frac{s-s_0}{t-t_0}$. The alternatives use incorrect addition or reverse the displacement sign.

10. Regarding average velocity and average speed, which proposition(s) are correct?

A. Average speed uses total distance divided by total time.

B. Average velocity is determined from the final position alone.

C. Average velocity uses total distance divided by total time.

D. Average speed uses displacement divided by elapsed time.

E. Average velocity uses displacement divided by elapsed time.

Answer: (A), (E)

Explanation

Average velocity is based on vector displacement over elapsed time, whereas average speed uses scalar total distance over total time. The other statements interchange these definitions or omit the required positional change.

11. Instantaneous velocity describes which physical quantity?

A. The velocity of a body at a particular instant.

B. The total distance traveled during motion.

C. The change in velocity divided by elapsed time.

D. The velocity of a body over a complete journey.

E. The average speed calculated over a time interval.

Answer: (A)

Explanation

Instantaneous velocity is the velocity at a specific instant or over an infinitesimally short interval. A complete journey concerns average quantities, while change in velocity divided by time defines acceleration.

12. Concerning acceleration, tick the correct proposition(s):

A. Acceleration is calculated from position divided by elapsed time.

B. An object accelerates when its speed increases, but not when it slows down.

C. An object accelerates when its direction changes.

D. Acceleration is the rate of change of velocity with time.

E. Acceleration measures the distance traveled per unit time.

Answer: (C), (D)

Explanation

Acceleration is the rate of change of velocity with time, so an object accelerates when its direction changes. It also accelerates when it speeds up or slows down; position divided by time and distance divided by time describe velocity or speed rather than acceleration.

13. For average acceleration, which proposition(s) are correct?

A. The SI unit of acceleration is $\mathrm{m/s^2}$.

B. Average acceleration equals change in position divided by elapsed time.

C. Acceleration has the SI unit $\mathrm{m/s}$.

D. Average acceleration uses total distance divided by total time.

E. Average acceleration equals change in velocity divided by elapsed time.

Answer: (A), (E)

Explanation

Average acceleration is $a=\frac{\Delta v}{\Delta t}$ and its SI unit is $\mathrm{m/s^2}$. Change in position over time gives velocity, while total distance over time gives average speed.

14. An object is moving along a straight path and slowing down. Which proposition(s) are correct?

A. Its speed decreases during the motion.

B. Slowing down means the object has zero acceleration.

C. Its acceleration points opposite to its direction of motion.

D. Negative acceleration has the same meaning in every coordinate system.

E. Its acceleration points in the direction of motion while it slows down.

Answer: (A), (C)

Explanation

When an object slows down, its speed decreases and its acceleration points opposite to its direction of motion. Slowing down therefore does not mean zero acceleration, and a negative acceleration component depends on the chosen coordinate direction.

15. For one-dimensional motion with constant acceleration, which equations may be used?

A. The velocity relation is $v^2=v_0^2+2as$.

B. The velocity equation is $v=v_0+at$.

C. The displacement equation is $s=v_0t+at^2$.

D. The velocity relation is $v^2=v_0^2+as$.

E. The displacement equation is $s=v_0t+\frac{1}{2}at^2$.

Answer: (A), (B), (E)

Explanation

Constant-acceleration motion is described by $v=v_0+at$, $s=v_0t+\frac{1}{2}at^2$, and $v^2=v_0^2+2as$. The incorrect formulas omit the factor $\frac{1}{2}$ or use an incorrect coefficient.

16. In uniformly accelerated motion, which graph characteristics are correct?

A. The position–time graph is parabolic.

B. The velocity–time graph is a straight line.

C. The velocity–time graph is horizontal for every acceleration.

D. The acceleration–time graph is parallel to the time axis.

E. The position–time graph is necessarily a straight line.

Answer: (A), (B), (D)

Explanation

Uniform acceleration produces a parabolic position–time graph, a straight velocity–time graph, and a constant acceleration–time graph parallel to the time axis. A straight position graph describes constant velocity, while a horizontal velocity graph corresponds to zero acceleration.

17. What does the tangent slope of a position–time graph represent?

A. It gives the displacement over the full motion.

B. It gives the average speed over the interval.

C. It gives the instantaneous acceleration.

D. It gives the area under the velocity–time graph.

E. It gives the instantaneous velocity.

Answer: (E)

Explanation

The tangent slope of a position–time graph gives instantaneous velocity. Acceleration is obtained from the slope of a velocity–time graph, while areas and interval averages represent different quantities.

18. Two objects move in the same direction, with speeds $12\,\mathrm{m/s}$ and $7\,\mathrm{m/s}$. Which proposition(s) are correct about relative velocity?

A. The relative-speed magnitude is $5\,\mathrm{m/s}$.

B. Relative velocity is defined with respect to another object or observer.

C. For objects moving in opposite directions, relative speeds are subtracted.

D. The relative-speed magnitude is $19\,\mathrm{m/s}$.

E. For objects moving in the same direction, relative speeds are subtracted.

Answer: (A), (B), (E)

Explanation

Relative velocity is defined with respect to another object or observer and is found by subtracting signed velocities. For objects moving in the same direction, the relative-speed magnitude is the difference, $12-7=5\,\mathrm{m/s}$; opposite directions give the sum, $12+7=19\,\mathrm{m/s}$.

19. Regarding elasticity, which of the following statements are correct?

A. Elasticity describes permanent deformation remaining after force removal.

B. Elastic behavior differs from plastic behavior because recovery occurs after unloading.

C. Elasticity concerns recovery of both original shape and original size.

D. Elasticity is a reversible response to a deforming force.

E. Elasticity allows a material to recover its original shape after force removal.

Answer: (B), (C), (D), (E)

Explanation

Elasticity allows recovery of original shape and size and therefore describes a reversible response. Permanent deformation characterizes plasticity, not elasticity; the distinction from plastic behavior is the material’s recovery after unloading.

20. Plasticity is best characterized by which statements?

A. Plastic deformation is irreversible once the force has been removed.

B. Plasticity permits permanent deformation after the deforming force is removed.

C. Plasticity describes recovery to the original shape after unloading.

D. Plasticity can change a body’s shape or size permanently.

E. Plasticity represents a reversible elastic response.

Answer: (A), (B), (D)

Explanation

Plasticity involves permanent, irreversible deformation after force removal and can permanently alter shape or size. Recovery after unloading describes elasticity rather than plasticity.

21. Concerning the elastic limit, select the correct statements:

A. The elastic limit identifies the upper range of reversible deformation.

B. The elastic limit is the greatest deforming force compatible with elastic behavior.

C. The elastic limit measures the force required to begin any deformation.

D. A body below its elastic limit returns to its original state after unloading.

E. The elastic limit is reached when permanent deformation is already established.

Answer: (A), (B), (D)

Explanation

The elastic limit is the maximum deforming force for which elastic behavior is retained. Below it, the body returns to its original state; it does not mean that permanent deformation has already begun or that all deformation is prevented.

22. Regarding density, which propositions are correct?

A. The density formula is $\rho=\frac{m}{V}$.

B. Density is defined as mass per unit volume of a substance.

C. Density is a dimensionless ratio of two substance densities.

D. Increasing volume at fixed mass decreases density.

E. Density is calculated by multiplying mass by volume.

Answer: (A), (B), (D)

Explanation

Density is mass divided by volume, expressed by $\rho=\frac{m}{V}$. At fixed mass, increasing volume lowers density; a ratio of two densities instead describes specific gravity, and mass is not multiplied by volume.

23. Specific gravity has which characteristics?

A. Specific gravity is dimensionless because it is a density ratio.

B. Specific gravity is defined as mass divided by the substance volume.

C. Specific gravity carries units of kilograms per cubic metre.

D. Specific gravity commonly uses water at 4 °C as the standard.

E. Specific gravity compares a substance’s density with a standard density.

Answer: (A), (D), (E)

Explanation

Specific gravity is the ratio of a substance’s density to a standard density, commonly water at 4 °C. Such a ratio has no units; mass divided by volume is density, not specific gravity.

24. A force acts over an area in a solid. Concerning stress, which statements are correct?

A. Stress measures fractional deformation without reference to force.

B. Stress is the deforming force acting per unit area.

C. Stress has the SI unit $\mathrm{N/m^2}$.

D. Stress has the SI unit of joule.

E. Stress is calculated by $\sigma=F\times A$.

Answer: (B), (C)

Explanation

Stress is force divided by area, $\sigma=\frac{F}{A}$, and its SI unit is $\mathrm{N/m^2}$. Multiplying force by area gives the wrong relation, joule is an energy unit, and fractional deformation describes strain.

25. Which statements correctly describe strain?

A. Strain is the fractional deformation produced under stress.

B. Strain is a ratio of force to cross-sectional area.

C. Strain is the ratio of tensile stress to longitudinal deformation.

D. Strain is dimensionless because it compares deformation with an original dimension.

E. Strain is measured in newtons per square metre.

Answer: (A), (D)

Explanation

Strain represents fractional deformation and is dimensionless because it is a ratio of lengths or comparable dimensions. Newtons per square metre and force divided by area describe stress, while the stress-to-strain ratio defines Young modulus.

26. A body remains at rest without rotating. Which statements describe static equilibrium?

A. Static equilibrium describes motion with constant angular velocity.

B. Zero net force alone guarantees that a body cannot rotate.

C. Static equilibrium requires zero resultant torque as well as zero net force.

D. Static equilibrium requires zero net force on the body.

E. A statically equilibrated body remains at rest without tilting or rotating.

Answer: (C), (D), (E)

Explanation

Static equilibrium requires both zero net force and zero net torque, so the body remains at rest without tilting or rotating. Zero net force alone does not exclude rotation, and constant angular velocity describes motion rather than static equilibrium.

27. Concerning the first condition of equilibrium, choose the correct propositions:

A. In two dimensions, force balance requires $\sum F_x=0$ and $\sum F_y=0$.

B. The first condition prevents translational acceleration.

C. The first condition by itself guarantees that rotation is impossible.

D. The vector sum of all forces must equal zero.

E. The first condition requires the resultant external torque to equal zero.

Answer: (A), (B), (D)

Explanation

The first equilibrium condition is $\sum \vec{F}=0$, which in two dimensions gives zero sums along both coordinate axes and prevents translation. Zero torque is the second condition, and force balance alone does not guarantee the absence of rotation.

28. Regarding torque produced by a force, which statements are correct?

A. The lever arm and force determine the torque magnitude together with their angle.

B. For a perpendicular force, torque magnitude becomes $\tau=Fr$.

C. Torque magnitude is $\tau=Fr\sin\theta$.

D. Torque is independent of the force’s angle to the lever arm.

E. Torque is the twisting effect of a force about a pivot.

Answer: (A), (B), (C), (E)

Explanation

Torque is the twisting effect about a pivot and has magnitude $\tau=Fr\sin\theta$. For a perpendicular force, this reduces to $\tau=Fr$; therefore, the angle affects torque and cannot be disregarded.

29. Regarding static equilibrium, which of the following statements are correct?

A. A body in static equilibrium remains at rest without tilting or rotating.

B. A rotating object can remain in static equilibrium when its angular speed is constant.

C. A body moving at constant velocity satisfies the definition of static equilibrium.

D. Static equilibrium requires the object to remain at rest rather than move uniformly.

E. A stationary object may be in static equilibrium when it does not tilt or rotate.

Answer: (A), (D), (E)

Explanation

Static equilibrium describes a body that remains at rest without tilting or rotating. Uniform motion and constant rotation do not satisfy this definition, so those descriptions are incorrect.

30. The first condition for static equilibrium is expressed by which statements?

A. The first condition concerns the balance of forces acting on the body.

B. The vector sum of all external forces must equal zero.

C. The first equilibrium condition requires balanced torques about an arbitrary axis.

D. A body satisfies the first condition when its total torque equals zero.

E. The equilibrium condition can be written as $\sum \vec{F}=0$.

Answer: (A), (B), (E)

Explanation

The first equilibrium condition balances all external forces, written as $\sum \vec{F}=0$. Torque balance belongs to the second condition, not the first.

31. Concerning the second condition of static equilibrium, select the correct statements:

A. Torques may be calculated about any arbitrary axis for this condition.

B. The second condition applies when the body moves at constant velocity.

C. The mathematical form of the condition is $\sum \tau=0$.

D. The second condition requires the vector sum of external forces to vanish.

E. The sum of all torques must equal zero.

Answer: (A), (C), (E)

Explanation

The second condition requires zero total torque, expressed as $\sum \tau=0$. The torques can be calculated about any arbitrary axis, and their sum must equal zero. This condition concerns rotational balance rather than motion at constant velocity; force balance describes the first condition.

32. Which statements correctly describe conservation of electric charge?

A. The total charge of an isolated system remains constant.

B. The conservation law states that charge is not destroyed in an isolated system.

C. Charge conservation permits charge to be created within an isolated system.

D. Charge may be transferred without changing the total charge of an isolated system.

E. Charge conservation requires the total charge to change when objects exchange electrons.

Answer: (A), (B), (D)

Explanation

In an isolated system, total electric charge remains constant because charge is transferred rather than created or destroyed. Electron exchange changes where charge resides, not the system’s total charge.

33. For the quantization of electric charge, identify the accurate statements:

A. Quantization means charge is expressed using integer multiples of $e$.

B. The quantity $n$ must be a positive real number.

C. Electric charge can be written as $q=ne$.

D. The symbol $e$ represents the magnitude of the elementary charge.

E. The integer $n$ may be positive or negative.

Answer: (A), (C), (D), (E)

Explanation

Charge quantization is described by $q=ne$, where $n$ is a positive or negative integer and $e$ is the elementary-charge magnitude. Thus charge occurs in integer multiples of $e$, not arbitrary positive real multiples.

34. The recognized methods for charging a body include which of the following?

A. Charging by rubbing is one established method.

B. Charging by radiation is one of the three listed methods.

C. Charging by conduction is one established method.

D. Charging by magnetic alignment is one of the three listed methods.

E. Charging by induction is one established method.

Answer: (A), (C), (E)

Explanation

The three listed charging methods are rubbing, conduction, and induction. Radiation and magnetic alignment are not included among these methods.

35. According to Coulomb’s law, which statements about electrostatic force are correct?

A. The force magnitude is proportional to the square of the separation distance.

B. Coulomb’s constant is approximately $9\times10^9\,\mathrm{N\,m^2/C^2}$.

C. The force magnitude is independent of the magnitudes of the two charges.

D. The force magnitude is proportional to the product of the charge magnitudes.

E. The force magnitude decreases with the square of the separation distance.

Answer: (B), (D), (E)

Explanation

Coulomb’s law is $F=k\frac{|q_1||q_2|}{r^2}$, so force increases with the charge-magnitude product and decreases with $r^2$. The stated approximate value of $k$ is correct, while distance is not a direct proportionality and charge magnitudes matter.

36. Regarding the direction and type of electrostatic force, select the correct statements:

A. Unlike charges attract one another.

B. Like charges repel one another.

C. The force acts along the line joining the two charges.

D. Like charges attract one another.

E. The electrostatic force acts perpendicular to the line joining the charges.

Answer: (A), (B), (C)

Explanation

Electrostatic force acts along the line joining the charges. Unlike charges attract, whereas like charges repel; therefore the perpendicular-direction statement is incorrect.

37. Electric field strength is correctly described by which statements?

A. Electric field strength is force per unit positive test charge.

B. Its magnitude can be calculated using $E=\frac{F}{q}$.

C. The definition uses a positive test charge.

D. The SI unit of electric field strength is coulomb per newton.

E. The SI unit of electric field strength is newton per coulomb.

Answer: (A), (B), (C), (E)

Explanation

Electric field strength is defined as force per unit positive test charge, $E=\frac{F}{q}$. Its SI unit is newton per coulomb, not coulomb per newton.

38. Which statements accurately describe an electric circuit?

A. A simple circuit includes a source, conducting wires, and a load.

B. An electric circuit is defined as a region where charges experience force.

C. Conducting wires form part of the simplest circuit arrangement.

D. A simple circuit consists of a source, insulating wires, and a load.

E. An electric circuit provides a path through which charges can flow.

Answer: (A), (C), (E)

Explanation

An electric circuit is a path for charge flow and, in its simplest form, contains a source, conducting wires, and a load. Insulating wires do not provide the required conducting path, and the region experiencing electric force defines a field.

39. Regarding electrical resistance, which statement or statements are correct?

A. Resistance describes the opposition presented by conductors and components.

B. Resistance supplies the driving force that produces electric current.

C. Resistance opposes the flow of electric charge through a conductor.

D. Resistance helps control the magnitude of current in a component.

E. Voltage is the property that directly opposes electric charge flow.

Answer: (A), (C), (D)

Explanation

Resistance opposes charge flow and controls current magnitude, so those statements are correct. Voltage drives current rather than opposing its flow, and resistance does not supply the driving force.

40. For a conductor obeying Ohm’s law, which statements are correct?

A. The resistance of a conductor drives the flow of electric charge.

B. The voltage across the conductor equals current multiplied by resistance.

C. Ohm’s law relates voltage, current, and resistance.

D. Georg Simon Ohm is associated with the law relating voltage, current, and resistance.

E. A conductor carrying $2\,\mathrm{A}$ through $5\,\Omega$ has a voltage of $10\,\mathrm{V}$.

Answer: (B), (C), (D), (E)

Explanation

Ohm’s law is $V=IR$, so the voltage equals current multiplied by resistance and the law relates voltage, current, and resistance. For $2\,\mathrm{A}$ through $5\,\Omega$, the voltage is $10\,\mathrm{V}$, and the law is associated with Georg Simon Ohm. Resistance opposes the flow of electric charge rather than driving it.

41. The resistance of a uniform conductor can be described by which statements?

A. Resistance decreases when its cross-sectional area becomes larger.

B. The relation includes the material resistivity, conductor length, and area.

C. Resistance is calculated as $R=\rho\frac{A}{L}$ for a uniform conductor.

D. A longer conductor has lower resistance when its area remains unchanged.

E. Resistance increases when the conductor becomes longer.

Answer: (A), (B), (E)

Explanation

For a uniform conductor, $R=\rho\frac{L}{A}$, so greater length raises resistance and greater area lowers it. The formula with area over length reverses the dependence, and increasing length does not lower resistance at fixed area.

42. Which statements correctly distinguish ohmic and non-ohmic materials?

A. A nonlinear current–voltage relationship indicates non-ohmic behavior.

B. Ohmic materials maintain approximately constant resistance over a wide voltage range.

C. Non-ohmic materials have a linear current–voltage relationship.

D. Non-ohmic materials exhibit a nonlinear current–voltage relationship.

E. Ohmic materials have a linear current–voltage relationship.

Answer: (A), (B), (D), (E)

Explanation

Ohmic materials show a linear current–voltage relationship and approximately constant resistance over a wide voltage range. Non-ohmic materials instead have nonlinear current–voltage behavior, so the linear description of them is incorrect.

43. Concerning series circuits, which statements are correct?

A. A series circuit provides one conducting path for current.

B. Opening one component can stop current throughout the circuit.

C. Every component in a series circuit lies along the same current path.

D. Current can continue through another branch after a series component opens.

E. A series circuit provides multiple independent paths for current.

Answer: (A), (B), (C)

Explanation

A series circuit has one conducting path, so opening a component interrupts current throughout the circuit. Multiple branches and continued current through another branch describe parallel arrangements, not a series circuit.

44. For resistors connected in series, which statements are correct?

A. The voltage is identical across every series resistor.

B. The equivalent resistance is $R_{eq}=R_1+R_2+\cdots+R_n$.

C. The same current passes through every series resistor.

D. The applied voltage is divided among the series resistors.

E. The total series resistance is found by multiplying all resistor values.

Answer: (B), (C), (D)

Explanation

Series resistors carry the same current, their voltages divide, and their equivalent resistance is the sum of their resistances. Equal voltage across each component and multiplication of resistor values are not series rules.

45. Which statements describe a parallel circuit?

A. A parallel circuit provides multiple conducting paths between common junctions.

B. Current may continue through other branches if one branch opens.

C. A parallel circuit has one conducting path shared by every component.

D. Opening one branch necessarily stops current in every remaining branch.

E. Different branches connect between the same pair of junctions.

Answer: (A), (B), (E)

Explanation

Parallel circuits contain multiple paths between common junctions, allowing current to continue in other branches when one opens. A single shared path and interruption of every branch are characteristics of series behavior.

46. For resistors connected in parallel, which statements are correct?

A. The equivalent resistance of parallel branches increases with each added branch.

B. The total current equals the sum of the branch currents.

C. The voltage is the same across every parallel branch.

D. The current is the same through every parallel branch.

E. The reciprocal equivalent resistance equals the sum of reciprocal branch resistances.

Answer: (B), (C), (E)

Explanation

In a parallel circuit, the voltage is the same across every branch, and the total current equals the sum of the branch currents. The reciprocal equivalent resistance equals the sum of the reciprocal branch resistances, so adding a branch lowers the equivalent resistance rather than increasing it. The current need not be the same through every branch.

47. Regarding the connection of electrical meters, which statements are correct?

A. An ammeter measures current in the circuit.

B. A voltmeter measures potential difference across a component.

C. A voltmeter is connected in parallel with the component.

D. Connecting an ammeter in parallel greatly increases circuit resistance.

E. An ammeter has high resistance to minimize its effect on circuit current.

Answer: (A), (B), (C)

Explanation

An ammeter measures current and is connected in series with the component, while a voltmeter measures potential difference and is connected in parallel. An ammeter has very low resistance, so placing it in parallel can cause excessive current and damage the meter; it does not greatly increase circuit resistance or have high resistance to minimize its effect.

48. Which statements correctly describe the resistance of electrical meters?

A. An ammeter has very low resistance to minimally change circuit current.

B. A voltmeter has very low resistance during measurement.

C. A voltmeter has high resistance to draw minimal current.

D. Meter resistance is selected to reduce disturbance of the measured circuit.

E. An ammeter has high resistance to prevent current from changing.

Answer: (A), (C), (D)

Explanation

A voltmeter’s high resistance minimizes the current it draws, while an ammeter’s low resistance minimizes its effect on circuit current. Reversing these resistance characteristics would disturb the circuit substantially.

49. Which statements correctly describe the effects of electric current on the body?

A. Approximately $100\,\mathrm{mA}$ through the body for a few seconds is usually harmless.

B. Currents above approximately $10\,\mathrm{mA}$ generally relax contracted hand muscles.

C. A current of $5\,\mathrm{mA}$ or less usually causes fatal cardiac effects.

D. Currents of $5\,\mathrm{mA}$ or less usually cause sensation with little or no damage.

E. Electric-shock severity is determined by current magnitude without regard to contact duration.

Answer: (D)

Explanation

Currents of $5\,\mathrm{mA}$ or less usually produce a shock sensation with little or no damage. Currents above about $10\,\mathrm{mA}$ can contract hand muscles, and about $100\,\mathrm{mA}$ for a few seconds can be fatal; duration also affects severity.

50. How does a fuse protect an electrical circuit?

A. Excessive current heats the fuse element.

B. Melting breaks the circuit and interrupts current flow.

C. The fuse restores conduction after an overload by cooling.

D. The fuse element melts when excessive current persists.

E. Short circuits and overloads can produce the excessive current that opens a fuse.

Answer: (A), (B), (D), (E)

Explanation

A fuse protects a circuit because excessive current heats and melts its element, breaking the circuit. It does not restore conduction after cooling; the interrupted fuse must be replaced.

51. Regarding magnets, which of the following statements are correct?

A. A magnetic field exists only around objects carrying electric current.

B. A magnet interacts with other objects through an electric field alone.

C. A magnet produces a magnetic field capable of attracting certain materials.

D. A magnet can attract or repel another magnet.

E. An ordinary unmagnetized material produces an equivalent magnetic field.

Answer: (C), (D)

Explanation

A magnet produces a magnetic field and can attract materials or attract and repel other magnets. Ordinary unmagnetized materials do not generally produce an equivalent magnetic field, and magnetic interaction is not explained by an electric field alone.

52. The characteristics of permanent magnets, temporary magnets, and electromagnets include:

A. Temporary magnets are defined by an iron core surrounded by a coil.

B. Permanent magnets require continuous current to maintain magnetization.

C. Electromagnets produce magnetic fields without current in their coils.

D. Temporary magnets retain magnetism after the external field is removed.

E. Permanent magnets retain their magnetic properties after magnetization.

Answer: (E)

Explanation

Permanent magnets retain their magnetic properties after magnetization. Temporary magnets lose magnetism when the external field is removed, while electromagnets produce fields when current flows through a coil around an iron core.

53. What happens when a magnet is cut into separate pieces?

A. Each resulting piece has both a North pole and a South pole.

B. One resulting piece contains a North pole and two South poles.

C. Cutting a magnet does not create an isolated magnetic pole.

D. Magnetic poles remain paired within every resulting piece.

E. The other resulting piece contains two North poles and a South pole.

Answer: (A), (C), (D)

Explanation

Every magnet has North and South poles, and magnetic poles occur in pairs. Therefore, cutting a magnet produces pieces that each contain both poles rather than isolated monopoles or pieces with unequal numbers of poles.

54. Concerning the origin and shape of Earth’s magnetic field, select the exact statement.

A. Movement of molten iron in Earth’s outer core generates the magnetic field.

B. The magnetic North pole coincides precisely with the geographic North Pole.

C. Earth’s magnetic field is generated mainly by solid rock in the crust.

D. Earth’s magnetic field is produced by atmospheric winds around the planet.

E. Earth’s field resembles a bar magnet aligned exactly with geographic poles.

Answer: (A)

Explanation

Movement of molten iron in the outer core generates Earth’s magnetic field. Its shape resembles a bar magnet tilted about 11 degrees from the geographic poles, so the magnetic and geographic poles do not coincide precisely.

55. A compass is used in navigation because it:

A. Contains a needle fixed permanently in one orientation.

B. Contains a magnetized needle that is free to turn.

C. Aligns its needle with the direction of a magnetic field.

D. Directly identifies geographic direction from the geographic poles.

E. Measures magnetic-field strength in teslas.

Answer: (B), (C)

Explanation

A compass contains a freely turning magnetized needle that aligns with the direction of a magnetic field. It indicates magnetic direction rather than directly defining geographic direction, and it is not a tesla meter.

56. For a long straight wire carrying current, which relationships are correct?

A. The field strength increases linearly with distance $d$ from the wire.

B. The field strength increases with the current $I$.

C. The field strength decreases as the distance $d$ increases.

D. The constant is $\mu_0 = 4\pi \times 10^{-7}\ \mathrm{T\,m\,A^{-1}}$.

E. The field strength is given by $B = \frac{\mu_0 I}{2\pi d}$.

Answer: (B), (C), (D), (E)

Explanation

For a long straight wire, $B = \frac{\mu_0 I}{2\pi d}$, so the field increases with current and decreases with distance. The stated value and units of $\mu_0$ are correct; the dependence on distance is inverse, not linear.

57. Regarding the magnetic field around a long straight current-carrying wire, which statements are correct?

A. The field lines form straight parallel paths along the wire.

B. Reversing the current reverses the magnetic-field direction.

C. The field lines are closed concentric circles around the wire.

D. The circles lie in planes perpendicular to the wire.

E. The field direction can be determined using the current direction.

Answer: (B), (C), (D), (E)

Explanation

A long straight current-carrying wire produces closed concentric circular field lines in perpendicular planes. Reversing the current reverses the field direction, whereas the field lines do not form straight paths along the wire.

58. For a charge moving through a magnetic field, which statements are correct?

A. The force direction is determined by the left-hand rule.

B. The force is maximum when the velocity is perpendicular to the field.

C. The force is independent of the charge speed $v$.

D. The force is zero when the velocity is parallel to the field.

E. The force magnitude is $F=qvB\sin\theta$.

Answer: (B), (D), (E)

Explanation

The magnetic force on a moving charge is $F=qvB\sin\theta$. It vanishes for parallel motion because $\sin 0=0$ and is maximum for perpendicular motion because $\sin 90^\circ=1$; it depends on speed. Its direction is perpendicular to the plane formed by the velocity and magnetic field and is determined by the right-hand rule.

59. A current-carrying wire placed in a uniform magnetic field experiences which effects?

A. Its force magnitude is $F=ILB\sin\theta$.

B. The force depends on the wire length $L$ and current $I$.

C. The force is independent of the angle between wire and field.

D. A wire carrying no current experiences the stated magnetic force.

E. A stationary uncharged wire experiences the same magnetic force.

Answer: (A), (B)

Explanation

The force on a current-carrying wire is $F=ILB\sin\theta$, so it depends on length, current, field strength, and angle. A stationary uncharged wire or a wire carrying no current does not experience this current-related magnetic force.

60. Parallel current-carrying wires interact according to which statements?

A. Two parallel wires carrying currents in opposite directions repel.

B. The interaction depends on the wires being charged but not carrying current.

C. Parallel wires repel when their currents have the same direction.

D. Two parallel wires carrying currents in the same direction attract.

E. Parallel wires attract when their currents have opposite directions.

Answer: (A), (D)

Explanation

Parallel wires with currents in the same direction attract, while wires with currents in opposite directions repel. The interaction is determined by the current directions, not by static charge alone.

61. Which statements distinguish mechanical waves from electromagnetic waves?

A. Electromagnetic waves can travel through empty space.

B. Mechanical waves require matter to transfer energy.

C. Mechanical waves propagate through a vacuum without matter.

D. Electromagnetic waves can travel through matter as well as empty space.

E. Electromagnetic waves require a material medium for propagation.

Answer: (A), (B), (D)

Explanation

Mechanical waves require matter to transfer energy. Electromagnetic waves can propagate through empty space and can also travel through matter, so they do not require a material medium.