Instructions
Read each question carefully. For the objective questions, circle the best answer. For the subjective and problem-solving questions, write your answers in complete sentences in the space provided or on a separate sheet of paper.
Part A: Objective Questions
- The bending of light as it passes from one substance (medium) to another is called:
- A) Reflection
- B) Absorption
- C) Refraction
- D) Diffraction
- Refraction occurs because light changes its ________ as it enters a new medium.
- A) Color
- B) Speed
- C) Brightness
- D) Source
- A substance that causes light to travel more slowly is described as being optically ________.
- A) Rarer
- B) Denser
- C) Brighter
- D) Darker
- When a ray of light travels from air into water, it bends:
- A) Towards the normal
- B) Away from the normal
- C) It does not bend
- D) It splits into two rays
- What is the 'normal' in a refraction diagram?
- A) The ray of light
- B) The surface of the medium
- C) A regular amount of light
- D) An imaginary line perpendicular to the surface
- Which of the following is an example of reflection, NOT refraction?
- A) A straw looking bent in a glass of water
- B) Seeing your face in a still pond
- C) A magnifying glass making letters look bigger
- D) The formation of a rainbow
- The angle between the incoming light ray and the normal is known as the angle of:
- A) Refraction
- B) Reflection
- C) Incidence
- D) Bending
- In which of the following does light travel the fastest?
- A) Water
- B) Glass
- C) Diamond
- D) A vacuum (empty space)
- The bottom of a swimming pool appears shallower than it actually is. This is due to:
- A) Reflection
- B) Refraction
- C) Absorption
- D) Dispersion
- A lens that is thicker at the edges and thinner in the middle is a:
- A) Convex lens
- B) Prism
- C) Concave lens
- D) Flat lens
- When light travels from glass (a denser medium) back into air (a rarer medium), it bends:
- A) Towards the normal
- B) Away from the normal
- C) Not at all
- D) It stops completely
- A ray of light will not refract if it strikes the boundary between two media at an angle of:
- A) 0 degrees (along the normal)
- B) 30 degrees
- C) 45 degrees
- D) 60 degrees
- The separation of white light into its different colors (like a rainbow) is called:
- A) Inversion
- B) Convergence
- C) Dispersion
- D) Interference
- When white light passes through a prism, which color of light bends the most?
- A) Red
- B) Green
- C) Yellow
- D) Violet
- A substance that allows light to pass through it is called a:
- A) Medium
- B) Block
- C) Reflector
- D) Opaque object
- Compared to diamond, water is an optically ________ medium.
- A) Denser
- B) Rarer
- C) Equal
- D) Darker
- The twinkling of stars is caused by the continuous ________ of starlight as it passes through the Earth's moving atmosphere.
- A) Reflection
- B) Blocking
- C) Refraction
- D) Creation
- A convex lens causes parallel light rays to:
- A) Spread apart (diverge)
- B) Come together (converge)
- C) Stop
- D) Bounce back
- Lenses in eyeglasses work because of the principle of:
- A) Reflection
- B) Absorption
- C) Refraction
- D) Color
- True or False: Refraction would not happen if light traveled at the same speed in all substances.
- A) True
- B) False
Part B: Subjective Questions
- In your own words, define what the refraction of light is.
- Explain why a pencil placed in a glass of water appears to be bent at the water's surface.
- What is the "normal" line, and why is it important when describing refraction?
- What is the difference between an optically rarer medium and an optically denser medium? Give one example of each.
- How does a simple magnifying glass use refraction to make objects appear larger?
- Briefly explain what causes a rainbow to form after it rains.
- Describe what happens to a single ray of light when it passes from air, through a rectangular glass block, and back out into the air.
- If a ray of light hits a glass surface perfectly straight on (at a 90° angle to the surface), why doesn't it bend?
- Name two everyday devices, besides eyeglasses, that rely on the refraction of light to function.
- State the main difference between the reflection of light and the refraction of light.
Part C: Problem-Solving Questions
- A lifeguard is sitting in a tall chair looking down at a swimmer on the bottom of the pool. Due to refraction, does the swimmer appear to be at their actual depth, deeper than they are, or shallower than they are? Explain your answer.
- You are standing on the bank of a clear, shallow river trying to spear a fish. To hit the fish, should you aim your spear directly at the image of the fish you see, slightly above the image, or slightly below the image? Explain your reasoning.
- On a separate piece of paper, draw a simple diagram showing a laser beam traveling from air into a block of clear gelatin (which is denser than air). Your diagram must include and label: the surface, the normal, the incident ray, and the refracted ray. In a sentence, describe whether the ray bends towards or away from the normal.
- On a very hot day, the road far ahead can sometimes look like there's a shimmering puddle of water on it. This is a mirage. How can refraction of light passing through layers of hot and cool air create this illusion?
- When sunlight passes through a raindrop, it splits into the colors of the rainbow. Explain why violet light is always on the inside of the rainbow's arc and red light is on the outside. (Hint: It relates to how much each color bends.)
Answer Key
Part A: Objective Questions
- C) Refraction
- B) Speed
- B) Denser
- A) Towards the normal
- D) An imaginary line perpendicular to the surface
- B) Seeing your face in a still pond
- C) Incidence
- D) A vacuum (empty space)
- B) Refraction
- C) Concave lens
- B) Away from the normal
- A) 0 degrees (along the normal) (Note: This means it passes straight through without bending)
- C) Dispersion
- D) Violet
- A) Medium
- B) Rarer
- C) Refraction
- B) Come together (converge)
- C) Refraction
- A) True
Part B: Subjective Questions
- Refraction is the bending of light when it passes from one medium (like air) into another (like water).
- The pencil appears bent because the light rays coming from the part of the pencil in the water refract, or bend, as they leave the water and enter the air before reaching your eyes. Your brain thinks the light traveled in a straight line, so the submerged part of the pencil appears to be in a different location.
- The normal is an imaginary line drawn at a 90° angle (perpendicular) to the surface where the light ray hits. It is important because the angles of incidence and refraction are measured from this line, which helps us predict how the light will bend.
- An optically denser medium is one where light travels more slowly (e.g., glass, water, diamond). An optically rarer medium is one where light travels faster (e.g., air, vacuum).
- A magnifying glass is a convex lens. It bends the light rays coming from an object so that they spread out (diverge). Our eyes trace these rays back to a point where they seem to originate, creating a larger, virtual image of the object.
- A rainbow is caused by the refraction and dispersion of sunlight through tiny water droplets in the air. As sunlight enters a raindrop, it refracts and splits into its colors. It then reflects off the back of the raindrop and refracts again as it leaves, separating the colors even more.
- When the light ray enters the glass block from the air, it slows down and bends towards the normal. It travels in a straight line through the glass. When it exits the glass block back into the air, it speeds up and bends away from the normal.
- If a light ray strikes a surface at 90°, its angle of incidence (the angle to the normal) is 0°. At this angle, the light changes speed but its path is not deviated, so it passes straight through without bending.
- Possible answers include: camera, microscope, telescope, binoculars, projector.
- Reflection is when light bounces off a surface (like a mirror). Refraction is when light bends as it passes through a surface into a new medium (like light going through a lens).
Part C: Problem-Solving Questions
- The swimmer appears to be shallower than they really are. The light rays traveling from the swimmer leave the water (denser medium) and bend away from the normal as they enter the air (rarer medium) to reach the lifeguard's eyes. The lifeguard's brain interprets these bent rays as having traveled in a straight line from a shallower location.
- You should aim your spear slightly below the image of the fish you see. This is because of refraction. The light from the fish bends as it leaves the water. This makes the fish appear to be in a shallower, different position (the apparent position) than its actual position. The fish is actually deeper than it appears.
- (Description of the correct drawing) The diagram should show a straight line (incident ray) in the "air" section hitting the surface at an angle. A dotted line (the normal) should be drawn perpendicular to the surface at that point. Inside the "gelatin" section, the refracted ray should be shown bent towards the normal. The ray bends towards the normal because it slows down upon entering the denser medium.
- The air near a hot road is very hot and less dense, while the air above it is cooler and denser. Light from the sky travels down towards the road, passing through layers of air with decreasing density. This causes the light to continually refract and bend upwards. When this bent light reaches your eye, your brain thinks it came straight from the ground, creating an illusion of a reflection on a wet surface.
- This happens because of dispersion. When sunlight enters a raindrop, different colors of light bend by slightly different amounts. Violet light has a shorter wavelength and is slowed down more than red light, so it bends the most. Red light has the longest wavelength and bends the least. This difference in bending angles separates the colors, and because of the angles involved, we see violet on the inside of the arc and red on the outside.