Flashcards: Electromagnetic Waves and Optics — 82 cards

What defines a scalar quantity in physics?

A single number and an appropriate unit specify it.

What two components specify a vector quantity?

Magnitude and direction specify it.

What does the magnitude of a vector represent graphically?

The length of its arrow when drawn to scale.

What is the first step in drawing a vector graphically?

Choose and record a scale.

What is the resultant vector?

A single vector with the same effect as combined vectors.

What is the formula for the resultant of vectors A and B?

$\mathbf{R}=\mathbf{A}+\mathbf{B}$.

How is subtracting vector B from vector A expressed?

$\mathbf{A}-\mathbf{B}=\mathbf{A}+(-\mathbf{B})$.

What are the rectangular components of vector A at angle $\theta$?

$A_x=A\cos\theta$ and $A_y=A\sin\theta$.

What defines the position of an object relative to a reference?

Its location relative to an origin or reference frame.

How does distance differ from displacement in motion?

Distance is scalar total path length; displacement is vector difference of positions.

What formula expresses displacement from initial to final position?

$\Delta s = s - s_0$

How is average velocity defined in terms of displacement and time?

Displacement divided by the time interval of that displacement.

What is the formula for average velocity using positions and times?

$v_{av} = \frac{\Delta s}{\Delta t} = \frac{s - s_0}{t - t_0}$

How is average speed calculated in terms of total distance and total time?

$v_{av}=\frac{s_{tot}}{t_{tot}}$

What defines instantaneous velocity?

Velocity at a specific instant or over an infinitesimally small time interval.

What is acceleration in terms of velocity and time?

The rate of change of velocity with time.

How is average acceleration calculated using velocity and time?

$a=\frac{\Delta v}{\Delta t}=\frac{v-v_0}{t-t_0}$

What is the SI unit of average acceleration?

Meters per second squared ($\mathrm{m/s^2}$).

In which direction does acceleration point when an object speeds up?

In the direction of motion.

In which direction does acceleration point when an object slows down?

Opposite to the direction of motion.

What is the equation relating velocity, initial velocity, acceleration, and time?

$v=v_0+at$

What shape is the position–time graph in uniformly accelerated motion?

A parabolic curve.

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

Instantaneous velocity.

What does the slope of a velocity–time graph indicate?

Acceleration.

What does the area under a velocity–time graph represent?

Displacement.

How is relative velocity defined?

Velocity of one object with respect to another object or observer.

What is the formula for relative velocity of object A with respect to B?

$v_{AB} = v_A - v_B$.

How do you find relative speed magnitude for objects moving in opposite directions?

Sum of their speeds.

What property allows a material to regain shape after force removal?

Elasticity

What is the ability to undergo permanent deformation after force removal?

Plasticity

What defines the maximum force for elastic behavior in a body?

Elastic limit

What is the definition of density in physics?

Mass of a substance per unit volume.

How is specific gravity defined?

Ratio of a substance's density to a standard substance's density.

What is the formula for calculating specific gravity?

$SG=\frac{\rho_{\mathrm{substance}}}{\rho_{\mathrm{water}}}$

How is stress defined and calculated?

Deforming force per unit area, $\sigma=\frac{F}{A}$.

What is strain in material science?

Fractional deformation produced under stress, dimensionless.

What is Young modulus and its formula?

Ratio of tensile stress to tensile strain, $Y=\frac{\text{tensile stress}}{\text{tensile strain}}$.

What defines static equilibrium in a body?

Net force and net torque are both zero, with no tilting or rotation.

What is the first condition of equilibrium regarding forces?

The vector sum of all forces equals zero.

How is the first equilibrium condition expressed in two dimensions?

As $\sum F_x=0$ and $\sum F_y=0$.

What is torque and how is its magnitude calculated?

Torque is a force's twisting effect about a pivot, calculated as $\tau=Fr\sin\theta$.

What is the simplified torque formula when force is perpendicular to the lever arm?

$\tau=Fr$

What is the second condition of equilibrium regarding torque?

The resultant external torque about an axis is zero.

How is the second equilibrium condition expressed mathematically?

As $\sum\tau=0$, balancing clockwise and counterclockwise torques.

What defines static equilibrium for an object or system?

It remains at rest without tilting or rotating.

What are the two types of electric charge and their carriers?

Positive charge is carried by protons and negative charge by electrons.

What does the law of conservation of charge state about total charge in an isolated system?

The total electric charge never changes in an isolated system.

What is the formula expressing quantization of electric charge?

$q=ne$ where $n$ is an integer and $e$ is the elementary charge.

What are the three methods of charging a body?

Charging by rubbing, conduction, and induction.

How does charging by conduction differ from charging by induction in sign of charge?

Conduction leaves both bodies with the same charge sign; induction gives opposite signs.

What formula expresses Coulomb's law for electrostatic force magnitude?

$F=k\frac{|q_1||q_2|}{r^2}$

Along which line does the electrostatic force act between two charges?

Along the line joining the two charges.

What is an electric field?

A region where an electric charge experiences an electric force.

What is the formula for electric field strength and its SI unit?

$E=\frac{F}{q}$ and newton per coulomb.

What components make up the simplest electric circuit?

A source, conducting wires, and a load.

What formula defines electric current and its SI unit?

$I=\frac{\Delta Q}{\Delta t}$ and ampere.

Name three examples of scalar quantities.

Time, distance, and speed.

Name three examples of vector quantities.

Displacement, velocity, and acceleration.

What magnitude does a unit vector have?

Magnitude one.

How does the triangle method find the resultant vector?

By placing each vector's head at the next vector's tail and joining first tail to last head.

What is the total distance and displacement magnitude for 60 km forward and 25 km back?

Distance is 85 km; displacement magnitude is 35 km.

What are displacement and total distance for 70 m east then 30 m west?

Displacement is 40 m east; total distance is 100 m.

What does a car’s speedometer reading represent?

The magnitude of its instantaneous velocity.

When does average speed equal the magnitude of average velocity?

During motion in the same direction along a straight line.

What defines uniformly accelerated motion?

Velocity changes by equal amounts in equal time intervals along a straight line.

What is the approximate free-fall acceleration near Earth's surface ignoring air resistance?

$9.80\,\mathrm{m/s^2}$ downward.

What does the area under an acceleration–time graph give?

Change in velocity.

What is an external force that changes a body's shape or size called?

Deforming force

Why must machine parts be kept below the elastic limit?

To maintain elastic behavior and avoid permanent deformation

How is the elastic limit used in selecting crane-rope thickness?

It helps determine thickness using the elastic limit and factor of safety

Why can long-used bridges become unsafe due to elasticity?

Repeated strains cause loss of elastic behavior

How does Earth's elasticity help estimate maximum mountain height?

By analyzing Earth's elastic behavior to estimate height limits

What is the SI unit of density?

Kilogram per cubic meter (kg/m³).

What is the conversion between kg/m³ and g/cm³ for density?

1 kg/m³ equals 10⁻³ g/cm³.

Why are two children of different masses balanced on a seesaw at different distances?

Because their opposite torques are equal.

How is torque defined in relation to force and distance?

Torque equals distance from pivot times perpendicular force component.

What equation represents torque balance in the seesaw example?

$m_Ag(2.5\,\mathrm{m}) - m_Bg(x) = 0$

How far must a 25 kg child sit to balance a 30 kg child at 2.5 m?

3.0 meters from the pivot.

What is an electroscope used to detect and measure?

Presence and type of charge, conductor or insulator, and quantity of charge.

What is electrical discharge and its effect on a charged body?

Rapid charge transfer that makes the body neutral through a conductor.

What formula gives the magnitude of the electric field from a point charge?

$E=k\frac{|q|}{r^2}$

What distinguishes a closed circuit from an open circuit?

A closed circuit has a complete path allowing current flow; an open circuit has a broken path and no current.