Quiz: Light and Optics
Test your understanding of light and optics with these 10 questions.
1. What is the law of reflection?
- The angle of reflection is larger than the angle of incidence
- The angle of reflection equals the angle of incidence
- Light cannot be reflected from smooth surfaces
- The angle of reflection depends on the light's color
Show Answer
The correct answer is B. The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal (perpendicular) to the surface. This law applies to all smooth reflecting surfaces and is independent of wavelength. It's the principle behind mirrors and reflective surfaces.
Concept Tested: Law of Reflection
2. What is refraction?
- The bouncing of light off a surface
- The bending of light when it passes from one medium to another
- The spreading of light through diffraction
- The polarization of light waves
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The correct answer is B. Refraction is the bending of light when it travels between media of different optical densities. Light changes speed when entering a new medium, causing it to bend. This is why objects appear bent when viewed through water, and why lenses can focus light.
Concept Tested: Refraction
3. How are the angles of incidence and refraction related?
- The angles are always equal
- Snell's Law: n₁sin(θ₁) = n₂sin(θ₂)
- The refracted angle is always larger
- There is no mathematical relationship
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The correct answer is B. Snell's Law relates the angles of incidence and refraction to the refractive indices of the two media: n₁sin(θ₁) = n₂sin(θ₂). This accounts for the change in light speed when entering a different medium. If light enters a denser medium (larger n), it bends toward the normal.
Concept Tested: Snell's Law
4. Light travels from air (n=1) into water (n=1.33) at an angle of 45° to the normal. What is the refracted angle?
- 30°
- 32°
- 45°
- 59°
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The correct answer is B. Using Snell's Law: (1)sin(45°) = (1.33)sin(θ₂). 0.707 = 1.33sin(θ₂). sin(θ₂) = 0.531. θ₂ ≈ 32°. Light bends toward the normal when entering a denser medium, so the refracted angle is smaller than the incident angle.
Concept Tested: Snell's Law
5. What is the difference between a converging lens and a diverging lens?
- They are the same thing
- Converging lenses are thicker in the middle and focus light; diverging lenses are thinner in the middle and spread light
- Converging lenses are larger than diverging lenses
- Diverging lenses can only be used for magnification
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The correct answer is B. Converging (convex) lenses are thicker in the middle and focus parallel rays to a focal point. They create real, inverted images and are used in cameras and magnifying glasses. Diverging (concave) lenses are thinner in the middle and spread light outward. They create virtual, upright images and are used in eyeglasses for nearsightedness.
Concept Tested: Lenses
6. What is the focal length of a lens?
- The length of the lens
- The distance from the lens where parallel rays converge (or appear to come from)
- The distance an object must be placed from the lens
- The size of the image produced
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The correct answer is B. The focal length (f) is the distance from the lens center where parallel rays converge (for converging lenses) or appear to diverge from (for diverging lenses). It's a property of the lens determined by its shape and the material's refractive index. Shorter focal lengths create stronger magnification.
Concept Tested: Lenses
7. A converging mirror with radius of curvature R = 20 cm reflects parallel light rays. Where do they converge?
- At 5 cm from the mirror
- At 10 cm from the mirror
- At 20 cm from the mirror
- They don't converge
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The correct answer is B. For a spherical mirror, the focal length f = R/2 = 20/2 = 10 cm. Parallel rays converge at the focal point, 10 cm from the mirror. This is the same principle as converging lenses and is used in telescopes, headlights, and satellite dishes.
Concept Tested: Mirrors
8. What is diffraction in the context of light?
- The reflection of light from surfaces
- The refraction of light through lenses
- The bending of light around obstacles or through small openings
- The splitting of light into colors
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The correct answer is C. Light diffraction is most noticeable when light passes through small openings or around small obstacles (comparable to the wavelength). Unlike refraction through lenses, diffraction cannot focus light. Single-slit and double-slit diffraction patterns demonstrate wave properties of light.
Concept Tested: Diffraction
9. What is polarization of light?
- The separation of light into different colors
- The alignment of light waves to oscillate in a particular direction
- The focusing of light by a lens
- The speed of light in a medium
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The correct answer is B. Polarization is the restriction of light wave oscillations to particular directions. Unpolarized light oscillates in all directions perpendicular to propagation. Polarizing filters allow only specific oscillation directions to pass. Polarized sunglasses reduce glare by blocking horizontally polarized light reflecting off water.
Concept Tested: Polarization
10. How does the wave-particle duality of light affect its behavior?
- Light is always a particle, never a wave
- Light exhibits wave properties when observed one way and particle properties another way depending on experimental setup
- Light's wave and particle properties occur simultaneously
- The duality is only theoretical with no practical applications
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The correct answer is B. Light exhibits complementary properties—in some experiments it behaves like a wave (diffraction, interference, polarization), while in others it behaves like particles called photons (photoelectric effect, energy transfer). The observed behavior depends on how we set up the experiment. This quantum duality is fundamental to modern physics.
Concept Tested: Wave-Particle Duality