Quiz: Fundamentals of Wave Optics and Cosmology — 18 domande

1. What does the relation v = fbb describe for a travelling wave?

A. Wave speed equals frequency multiplied by wavelength

B. Wavelength equals wave speed multiplied by frequency

C. Frequency equals wave speed multiplied by wavelength

D. Wave speed equals wavelength divided by frequency

Answer: (A)

Spiegazione

The wave-speed relation is v = fbb, so speed is the product of frequency and wavelength. The other options rearrange the relation incorrectly.

2. In a fixed medium where wave speed stays constant, what happens to the wavelength if the frequency increases?

A. The wavelength increases in direct proportion

B. The wavelength stays the same because only amplitude changes

C. The wavelength becomes equal to the frequency

D. The wavelength decreases so that v remains constant

Answer: (D)

Spiegazione

With v fixed, increasing f must reduce bb so that v = fbb still holds. This is the standard frequency-wavelength trade-off in the same medium.

3. What remains unchanged when a plane wave reflects from a boundary?

A. Its direction of propagation

B. Its frequency

C. Its speed in the original medium

D. Its wavelength in the new medium

Answer: (B)

Spiegazione

Reflection preserves the wave frequency. The direction changes, but the reflected wave keeps the same frequency as the incident wave.

4. Which statement best describes refraction of a plane wave at a boundary?

A. The wave reverses direction while keeping the same speed

B. The wave frequency changes because the medium changes

C. The wavefronts vanish because energy is absorbed

D. The wavefronts bend because the propagation speed changes

Answer: (D)

Spiegazione

Refraction is caused by a change in speed across the boundary, which bends the wavefronts. Frequency is not the defining change here.

5. In the thin-lens model, which ray passes through the optical center without changing direction?

A. A ray passing through the principal focus

B. A ray parallel to the principal axis

C. A ray aimed through the optical center

D. A ray reflected from the lens surface

Answer: (C)

Spiegazione

A ray through the optical center continues straight in the thin-lens approximation. The parallel and focus rays obey different principal-ray rules.

6. What does the thin-lens equation 1/u + 1/v = 1/f help determine?

A. The angular size of the principal axis

B. The image distance from the object distance and focal length

C. The color of the image formed by the lens

D. The speed of light in the lens material

Answer: (B)

Spiegazione

The thin-lens equation links object distance, image distance, and focal length. It is used with magnification to predict image formation.

7. What does the electromagnetic spectrum consist of?

A. A set of sound waves traveling through vacuum

B. Only the visible colors detectable by the eye

C. A list of charged particles moving in space

D. A range of electromagnetic radiation types ordered by frequency and wavelength

Answer: (D)

Spiegazione

The electromagnetic spectrum includes all electromagnetic radiation types arranged by frequency and wavelength. Visible light is only a small part of it.

8. What is used as evidence for an expanding universe in basic cosmology?

A. The daily motion of the stars

B. The changing phases of the Moon

C. Cosmological red-shift in line spectra

D. The constant speed of sound in air

Answer: (C)

Spiegazione

Cosmological red-shift in spectra supports the idea that distant galaxies are moving away, consistent with expansion. The other choices are unrelated to cosmological expansion.

9. What does the heliocentric model place at the center of the solar system?

A. The brightest star in the sky

B. The Sun

C. The Moon

D. The Earth

Answer: (B)

Spiegazione

In the heliocentric model, the Sun is at the center and the planets orbit it. This contrasts with Earth-centered models.

10. Which stellar property most strongly determines a star's evolutionary path and final state?

A. Distance from Earth

B. The number of planets around it

C. Surface color

D. Mass

Answer: (D)

Spiegazione

Mass is the key factor controlling stellar evolution and the star's end state. The other options do not determine the evolution path in the same way.

11. What is total internal reflection?

A. Absorption of light by a very dense material

B. Complete reflection at a boundary when the incidence angle exceeds the critical angle

C. Transmission of all light with no change in direction

D. Partial bending of a wave when it enters a new medium

Answer: (B)

Spiegazione

Total internal reflection occurs when the incidence angle is greater than the critical angle, so the wave is completely reflected. It is not the same as ordinary refraction.

12. Which optical instrument uses fibre optics to view internal body parts?

A. A prismatic periscope

B. An endoscope

C. A simple magnifying glass

D. A plane mirror

Answer: (B)

Spiegazione

An endoscope uses fibre optics to transmit light and image information inside the body. A prismatic periscope and a magnifying glass serve different purposes.

13. What is impulse equal to?

A. Force multiplied by the time interval

B. Mass multiplied by acceleration

C. Velocity multiplied by momentum

D. Distance multiplied by speed

Answer: (A)

Spiegazione

Impulse is the effect of a force acting over time, and it equals the change in momentum. This is why force over a longer time can change momentum in the same way with a smaller peak force.

14. What is momentum defined as?

A. Acceleration times distance

B. Mass times velocity

C. Force times time

D. Energy divided by mass

Answer: (B)

Spiegazione

Momentum is defined as p = mv. The force-time product is impulse, not momentum.

15. Which set contains the ferromagnetic elements listed in the course material?

A. Iron, nickel, and cobalt

B. Hydrogen, helium, and neon

C. Sodium, potassium, and calcium

D. Copper, silver, and gold

Answer: (A)

Spiegazione

The three ferromagnetic elements named are iron, nickel, and cobalt. The other groups are not the standard ferromagnetic set here.

16. What does a magnetic field line represent?

A. The outline of a magnet's physical shape

B. The direction of force on a north-seeking pole

C. The direction of gravity near a magnet

D. The path taken by an electric current

Answer: (B)

Spiegazione

Magnetic field lines show the field direction, taken as the direction of force on a north pole, and their spacing indicates relative strength. They are not physical paths traveled by current.

17. What is true for resistors connected in series?

A. The total resistance is always smaller than each resistor

B. The voltage across each component is the same

C. Each resistor carries a separate branch current

D. The same current flows through each component

Answer: (D)

Spiegazione

In a series circuit, the same current passes through every component. Equal voltage across components is a property of parallel connections.

18. What value does 230 V AC represent in basic circuit work?

A. The RMS value

B. The minimum instantaneous value

C. The average value over a cycle

D. The peak-to-peak value

Answer: (A)

Spiegazione

The stated 230 V AC is the RMS value, the effective voltage used for power comparisons. It is related to the peak value by V_rms = V_peak /   2.