Properties of Light

Properties of Light

• Light can be reflected.
• Light can be refracted.
• Light exhibits wave-particle duality.
• Light travels in straight lines.

Particle Model Evidence

• The photoelectric effect demonstrates that light can behave as a stream of particles (photons), knocking electrons off a metal surface.
• Sharp shadows indicate that light travels in straight lines and can be blocked by objects, behaving like particles.

Concert Lighting and Visibility

• An audience member can see the performer because light rays reflect off the performer's body in various directions, some reaching the audience member's eyes.
• Whether the audience member sees the light source depends on the angle; if light rays from the source directly enter their eyes, they will see it.
• Similarly, the performer can see the light source if light rays from it reach their eyes.
• Fog makes the light beam visible due to scattering; fog particles reflect light in various directions, including towards the observer.

Definitions

• Transparent materials allow light to pass through them, enabling clear vision through the material.
• Translucent materials allow some light to pass through but scatter it, so objects are not clearly visible through them.
• Opaque materials do not allow light to pass through; they absorb or reflect light.

Shadow Formation

• When an object moves closer to a light source, its shadow becomes larger and more blurred because it blocks a larger angle of light.

Umbra and Penumbra

• Umbra: The total shadow where all light is blocked.
• Penumbra: The partial shadow, which results from only some of the light being blocked.

Pinhole Camera

• The reproduction of the light bulb on the screen changes size depending on the distance of the screen from the pinhole: moving the screen farther away increases the image size, and moving the screen closer decreases the image size.

Pinhole Size and Image Quality

• Increasing the size of the pinhole increases the brightness of the image reproduction on the screen.
• Sharpness decreases with increasing pinhole size.
• Images appear upside-down in a pinhole camera because light rays from the top of an object pass through the pinhole and project to the bottom of the screen, and vice versa.

Light Intensity and Distance

• When a solar-powered space probe travels twice as far from the sun, the solar panels need to be four times larger to receive the same quantity of light from the sun.
• The intensity of light decreases with the square of the distance.

Sunlight Intensity Comparison

• Jupiter is five times farther from the Sun than Earth
• The intensity of sunlight striking Earth is 25 times greater than the intensity striking Jupiter.
• Intensity decreases with the square of the distance.

Sunlight Intensity Comparison for Venus

• Venus' orbital radius is 0.7 times Earth's orbital radius.
• The intensity of sunlight striking Earth is 0.49 times the intensity striking Venus.
• Intensity is proportional to the inverse square of the distance.

Horsehead Nebula Over Time

• The appearance of the Horsehead Nebula is likely different today because of the vast distance (1500 light-years).
• The light we see now left the nebula 1500 years ago, and the nebula may have changed significantly since then.

Reflection off a Mirror

• The diagram shows light rays reflecting off a mirror, with numbered rays and a normal line.

Angle of Incidence and Reflection

• Ray likely includes an error in the recording of results.
• Plot the data from the table on to the right on the right.
• The angle of incidence and angle of reflection should be equal when measured from the normal.