Physical Optics and Gravitational Waves

Physics · 11th Class (Intermediate Part 1) · BISE Lahore

70 questions

Tests for this chapter

Tests run in your chosen medium — the sample below shows both.

Full Book Test

20 questions · Measurements × 1, Force and Motion × 2, Circular and Rotational Motion × 2, Work, Energy and Power × 1, Solids and Fluid Dynamics × 2, Heat and Thermodynamics × 1, Waves and Vibrations × 3, Physical Optics and Gravitational Waves × 1, Electrostatics and Current Electricity × 3, Electromagnetism × 2, Special Theory of Relativity × 1, Nuclear and Particle Physics × 1

Physical Optics and Gravitational Waves Test

10 questions · Physical Optics and Gravitational Waves × 10

Sample questions

Showing 20 of 70 questions from this chapter. The full bank is in the chapter test below.

1
The phenomenon of polarization can be exhibited by
- A.only longitudinal waves
- B.only transverse waves (correct answer)
- C.waves of every kind
- D.only stationary waves
Why: In a transverse wave the vibrations are perpendicular to the direction of travel, so they can be confined to a single plane. A longitudinal wave vibrates along the direction of propagation and therefore cannot be polarized.
2
Polarization of light is the process by which
- A.the electric field vibrations of light are restricted to a single plane (correct answer)
- B.light is scattered by the molecules of the atmosphere
- C.light changes its speed on entering a denser medium
- D.white light is dispersed into its component colours
Why: Polarization restricts the electric field vibrations of a light wave to a single plane of vibration. Scattering, refraction and dispersion change the direction, speed or colour of light but do not by themselves confine the vibrations to one plane.
3
The plane of polarization of a wave is the plane that contains
- A.only the direction of propagation of the wave
- B.only the direction of vibration of the particles
- C.the wavefront and the direction of propagation
- D.both the direction of propagation and the direction of vibration (correct answer)
Why: The plane of polarization is fixed by two directions together: the direction in which the wave travels and the direction in which the vibrating quantity oscillates.
4
Which of the following sources emits unpolarized light?
- A.An incandescent light bulb (correct answer)
- B.Light that has passed through a polaroid sheet
- C.Light reflected from glass at the polarizing angle
- D.Light that has passed through a calcite crystal
Why: In an incandescent bulb the charges radiate randomly, so the electric field has components in all planes and the light is unpolarized. A polaroid sheet, a calcite crystal and reflection at the polarizing angle all restrict the vibrations and give partly or fully polarized light.
5
In ordinary unpolarized light, the electric field vector
- A.lies in one fixed plane that contains the ray
- B.is confined to two mutually perpendicular planes
- C.has components of vibration in all possible planes (correct answer)
- D.is parallel to the direction of propagation
Why: Ordinary light contains vibrations in every plane about the ray. Limiting the vibrations to one plane would make the light polarized, and an electric field parallel to the ray is impossible for a transverse wave.
6
Which of the following is NOT a method of polarizing unpolarized light?
- A.Passing it through a polaroid sheet
- B.Using a polarizing beam splitter
- C.Passing it through a calcite crystal
- D.Raising the temperature of the light source (correct answer)
Why: Polaroids, polarizing beam splitters and crystals such as calcite or quartz all confine the vibrations of light to one plane. Heating the source only changes the power and the spectrum of the emitted light; it does not polarize it.
7
When unpolarized light passes through a polaroid sheet, the light that emerges is
- A.still unpolarized
- B.plane polarized along the axis of the sheet (correct answer)
- C.circularly polarized
- D.completely absorbed
Why: A polaroid passes only the component of the electric field parallel to its axis and blocks the perpendicular components, so the emerging light is plane polarized. About half of the intensity is lost, but the beam is not absorbed completely.
8
In circularly polarized light, the electric field vector
- A.oscillates along a single straight line
- B.traces an ellipse whose two axes are unequal
- C.rotates about the direction of propagation with constant magnitude (correct answer)
- D.is parallel to the direction of propagation
Why: In circular polarization the tip of the electric vector rotates steadily, clockwise or anticlockwise, while its magnitude stays the same. A straight-line oscillation is linear polarization, and unequal axes give elliptical polarization.
9
Elliptical polarization of light is produced when the two perpendicular components of the electric field
- A.have unequal amplitudes or differ in phase by an arbitrary angle (correct answer)
- B.have equal amplitudes and are exactly in phase
- C.are equal in amplitude and exactly $90^{\circ}$ out of phase
- D.are both parallel to the direction of propagation
Why: Elliptical polarization is the general case: the two component amplitudes are unequal, or their phase difference is some arbitrary angle, so the tip of the electric vector traces an ellipse. Equal amplitudes with a $90^{\circ}$ phase difference give circular polarization instead.
10
Which of the following is an example of circularly polarized light?
- A.Light reflected from the surface of a compact disc (correct answer)
- B.Light passing through a polaroid sheet
- C.Light from an incandescent bulb
- D.Light passing through a sugar solution
Why: Light reflected from a compact disc or a DVD is the standard example of circular polarization. A polaroid sheet gives linear polarization, an incandescent bulb gives unpolarized light, and a sugar solution rotates the plane of light that is already polarized.
11
Light transmitted by ordinary polarizing sunglasses is
- A.circularly polarized
- B.elliptically polarized
- C.linearly polarized (correct answer)
- D.unpolarized
Why: The polaroid in the sunglasses transmits only the vibration parallel to its axis, so the emerging light is linearly polarized. That is why such glasses cut the glare from roads and water, which is partly polarized in the horizontal plane.
12
Which of the following produces elliptically polarized light?
- A.A polaroid sheet alone
- B.A candle flame
- C.An incandescent bulb
- D.A stress plate or a waveplate (correct answer)
Why: A stress plate or waveplate introduces a phase difference between the two components of the electric field, so the emerging light is elliptically polarized. A polaroid gives linear polarization, while a candle flame and an incandescent bulb give unpolarized light.
13
Two polaroid sheets are placed one behind the other in a beam of unpolarized light. When their axes are mutually perpendicular, the light emerging from the second sheet is
- A.of maximum intensity
- B.half of the incident intensity
- C.zero (correct answer)
- D.circularly polarized
Why: The first sheet polarizes the light and the second passes only the component parallel to its own axis; when the axes are perpendicular that component is zero, so no light gets through.
14
A polarizer is followed by a second polaroid sheet called the analyzer. The analyzer is used mainly to
- A.convert ordinary light into plane polarized light
- B.determine the intensity of the light transmitted by the polarizer (correct answer)
- C.increase the amplitude of the polarized beam
- D.rotate the plane of polarization through a right angle
Why: The light reaching the analyzer is already plane polarized, so observing the transmitted intensity as the analyzer is rotated tells us the intensity of that polarized beam. Converting ordinary light into polarized light is the task of the first polaroid.
15
When the axes of two polaroid sheets are made exactly perpendicular, the transmitted light falls to zero. This shows that light waves are
- A.longitudinal
- B.mechanical
- C.able to travel through a vacuum
- D.transverse (correct answer)
Why: A longitudinal wave has no transverse vibration that could be blocked, so crossed filters could never extinguish it. Complete extinction therefore proves that the light vibrations are perpendicular to the ray, that is light is transverse.
16
For light travelling from a medium of refractive index $n_1$ into a medium of refractive index $n_2$ , the polarizing angle $\theta_p$ satisfies
- A. $\sin\theta_p = n_2/n_1$
- B. $\cos\theta_p = n_2/n_1$
- C. $\tan\theta_p = n_2/n_1$ (correct answer)
- D. $\cot\theta_p = n_2/n_1$
Why: At the polarizing angle the reflected and refracted rays are at right angles, and applying Snell's law to that condition gives $\tan\theta_p = n_2/n_1$ , which is Brewster's law.
17
The polarizing angle for a glass surface of refractive index 1.5 in air is about
- A. $56.3^{\circ}$ (correct answer)
- B. $33.7^{\circ}$
- C. $48.8^{\circ}$
- D. $63.4^{\circ}$
Why: With light coming from air, $\tan\theta_p = n = 1.5$ , so $\theta_p = 56.3^{\circ}$ . The value $33.7^{\circ}$ is the angle of refraction, which is the complement of the polarizing angle.
18
At the polarizing angle, the reflected ray and the refracted ray are
- A.parallel to each other
- B.at right angles to each other (correct answer)
- C.at $45^{\circ}$ to each other
- D.at $60^{\circ}$ to each other
Why: The polarizing angle is defined by $\theta_p + r = 90^{\circ}$ , so the reflected and refracted beams are perpendicular to each other. That is exactly the condition that makes the reflected light plane polarized.
19
A beam of light is incident on a glass plate at the polarizing angle of $60^{\circ}$ . The angle of refraction of the light inside the glass is
- A. $30^{\circ}$ (correct answer)
- B. $45^{\circ}$
- C. $60^{\circ}$
- D. $90^{\circ}$
Why: At the polarizing angle the reflected and refracted rays are at right angles, so $r = 90^{\circ} - 60^{\circ} = 30^{\circ}$ . Snell's law checks this: with $n = \tan 60^{\circ} = 1.73$ , $n\sin 30^{\circ} = \sin 60^{\circ}$ .
20
The polarizing angle for a certain medium is $54.5^{\circ}$ . The refractive index of the medium is about
- A.1.2
- B.1.4 (correct answer)
- C.1.6
- D.1.8
Why: For light incident from air, $n = \tan\theta_p = \tan 54.5^{\circ} = 1.40$ . A refractive index of 1.6 would require a polarizing angle of about $58^{\circ}$ .

← All chapters of Physics