Science: Optics: Reflection, Refraction, and Lenses
How light reflects, bends, and forms images through lenses
Science: Optics: Reflection, Refraction, and Lenses
How light reflects, bends, and forms images through lenses
Physics - Grade 9-12
- 1
State the law of reflection. Then describe what happens to the angle of reflection when the angle of incidence increases.
Both angles are measured from the normal line, not from the surface.
The law of reflection states that the angle of incidence equals the angle of reflection, measured from the normal. When the angle of incidence increases, the angle of reflection increases by the same amount. - 2
A ray of light strikes a flat mirror at an angle of incidence of 35 degrees. What is the angle of reflection?
The angle of reflection is 35 degrees because the angle of reflection always equals the angle of incidence. - 3
Explain why an object appears to be behind a plane mirror. Include the idea of virtual images in your response.
Think about where the reflected rays seem to come from.
A plane mirror forms a virtual image because reflected light rays spread out in a way that makes the brain trace them backward to a point behind the mirror. The image appears behind the mirror even though no light actually comes from that location. - 4
Light travels from air into water at an angle. Does the light ray bend toward the normal or away from the normal? Explain why.
The light ray bends toward the normal when it enters water from air. This happens because light slows down in water, which has a higher optical density than air. - 5
Light travels from water into air at an angle. Describe how the ray bends and explain the reason.
Compare the speed of light in water and in air.
The light ray bends away from the normal when it moves from water into air. This happens because light speeds up as it enters the less optically dense medium. - 6
A student places a straw in a glass of water and observes that the straw appears bent at the water surface. Explain this observation using refraction.
The straw appears bent because light from the part of the straw under water changes direction as it passes from water into air. This refraction makes the underwater part appear shifted from its actual position. - 7
Define the index of refraction and explain what a larger index of refraction means about the speed of light in a material.
The index compares light speed in vacuum to light speed in the medium.
The index of refraction is a measure of how much light slows down in a material compared with its speed in a vacuum. A larger index of refraction means that light travels more slowly in that material. - 8
Describe the difference between a converging lens and a diverging lens in terms of shape and what happens to parallel light rays.
A converging lens is thicker in the middle than at the edges and causes parallel light rays to come together at a focal point. A diverging lens is thinner in the middle than at the edges and causes parallel light rays to spread apart as if they came from a focal point. - 9
An object is placed farther than one focal length from a converging lens. Describe one possible image that can form and state whether it is real or virtual.
A real image can be projected onto a screen.
When an object is placed farther than one focal length from a converging lens, one possible image is a real image that forms on the opposite side of the lens. This image can be inverted and may be larger or smaller depending on the object's distance from the lens. - 10
An object is placed inside the focal length of a converging lens. Describe the image that forms.
When an object is placed inside the focal length of a converging lens, the image is virtual, upright, and magnified. It appears on the same side of the lens as the object. - 11
Explain why a diverging lens always forms a virtual image for a real object.
Consider whether the refracted rays really cross.
A diverging lens spreads light rays apart after they pass through the lens, so the rays do not actually meet on the far side. The brain traces the rays backward to a point on the object's side of the lens, which creates a virtual image. - 12
A magnifying glass uses a converging lens. Explain how it makes small objects look larger.
A magnifying glass makes objects look larger by placing the object inside the focal length of a converging lens. This creates a virtual, upright, magnified image that appears larger to the observer.