AP Physics Waves & Optics — Questions and Answers
Question 1: What is the definition of a wave?
- A disturbance that causes particles to move
- A transfer of energy without matter movement (Correct answer)
- A force moving in one direction
- A moving particle
Correct answer: A transfer of energy without matter movement
A wave is fundamentally a disturbance that propagates through a medium or space, transferring energy from one point to another. Crucially, this transfer of energy occurs without the net transfer of matter; the particles of the medium oscillate about their equilibrium positions but do not travel along with the wave itself.
Question 2: What is the relationship between frequency and wavelength in a wave?
- Frequency is directly proportional to wavelength
- Frequency is inversely proportional to wavelength (Correct answer)
- Frequency has no effect on wavelength
- Frequency and wavelength are unrelated
Correct answer: Frequency is inversely proportional to wavelength
For a wave traveling at a constant speed (v), its frequency (f) and wavelength (λ) are inversely proportional, as described by the wave equation v = fλ. This means that if the frequency of a wave increases, its wavelength must decrease, and vice versa, to maintain a constant wave speed.
Question 3: What is refraction?
- Reflection of light
- Bending of light due to density change (Correct answer)
- Absorption of light
- Transmission of light
Correct answer: Bending of light due to density change
Refraction is the phenomenon where a wave, such as light, changes direction as it passes from one medium to another. This bending occurs because the wave's speed changes as it enters a medium with a different optical density, causing it to deviate from its original path according to Snell's Law.
Question 4: What is the main principle behind the Doppler effect?
- Light waves move faster
- Wave frequency changes due to relative motion (Correct answer)
- Speed of light varies with observation
- Sound waves cannot travel
Correct answer: Wave frequency changes due to relative motion
The Doppler effect describes the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. When the source and observer move closer, the frequency appears higher, and when they move apart, the frequency appears lower, due to the compression or stretching of the wavefronts.
Question 5: What does the law of reflection state?
- Angle of incidence does not equal angle of reflection
- Angle of incidence equals angle of reflection (Correct answer)
- Reflection causes a 90° angle change
- Reflection does not occur in flat surfaces
Correct answer: Angle of incidence equals angle of reflection
The law of reflection states that when a wave, such as light, strikes a surface, the angle at which it hits the surface (angle of incidence) is equal to the angle at which it bounces off (angle of reflection). Both angles are measured with respect to the normal, an imaginary line perpendicular to the surface.
Question 6: What is interference in waves?
- Waves travel independently of each other
- Two waves combine to form a new pattern (Correct answer)
- Waves cancel each other out
- Waves only add together
Correct answer: Two waves combine to form a new pattern
Wave interference occurs when two or more waves superpose, meaning they combine their amplitudes at each point in space. This superposition can result in a new wave pattern with either increased amplitude (constructive interference) or decreased amplitude (destructive interference), depending on their relative phases.
Question 7: What is diffraction?
- Reflection of light at edges
- Bending of waves around obstacles (Correct answer)
- Absorption of sound waves
- Transmission of light
Correct answer: Bending of waves around obstacles
Diffraction is the phenomenon where waves spread out or bend as they pass through an aperture or around the edges of an obstacle. This effect is more pronounced when the wavelength of the wave is comparable to the size of the opening or obstacle, causing the wave to deviate from a straight-line path.
Question 8: How does the frequency of light affect its color?
- Higher frequency corresponds to red
- Lower frequency corresponds to blue
- Higher frequency corresponds to violet (Correct answer)
- Frequency does not affect color
Correct answer: Higher frequency corresponds to violet
The color of visible light is determined by its frequency (or wavelength). Within the visible spectrum, light with higher frequencies corresponds to colors like blue and violet, while light with lower frequencies corresponds to colors like orange and red. Therefore, higher frequency light appears violet.
Question 9: What is the critical angle in refraction?
- The angle where light passes through without reflection
- The angle at which total internal reflection occurs (Correct answer)
- The angle of refraction at maximum speed
- The angle of incidence below which reflection occurs
Correct answer: The angle at which total internal reflection occurs
The critical angle is the specific angle of incidence in the denser medium at which the refracted ray travels along the boundary between two media. If the angle of incidence exceeds this critical angle, the light undergoes total internal reflection, meaning it is entirely reflected back into the denser medium rather than refracting out.
AP Physics Waves & Optics
What is the definition of a wave?