Question: We see the sun rising 81/4 minutes after it has actually risen. Why?
Answer: The distance from the sun to the earth is 1485 lakh Kilometers. We can calculate that light travels from the sun to the earth in 81/4 minutes. That means we see the sun rising 81/4 minutes after it has risen.
Question: Name two natural sources of light and two human-made sources of light.
Answer: Man made sources of light are – tube light and candle. Natural sources of light are – sun and firefly
Question: How do we see non-luminous objects?
Answer: Objects that do not produce their own light are called non-luminous objects. We can see non-luminous objects when,
- light falls on non-luminous objects, such as book
- The object should reflect light towards our eyes.
Question: To see an object what do we need?
Answer: To see any non-luminous object we need the following:
- Source of light
- an object
When a light emitting from luminous body falls on a non-luminous object and is reflected. This reflected light reaches our eyes enables us to see that object.
Question: Moon appears bright at night. Is it a luminous or non-luminous body?
Answer: Moon is a non-luminous body, it does not emit its own light. It reflects the sun light that falls on it.
Question: What is meant by rectilinear propagation of light?
Answer: The light that travels in straight line is called rectilinear propagation of light. For example: When we shine a torch in the dark, light appears to go straight outwards. Similarly the light from the cinema projector also appears to take a straight path to the screen.