Class Notes NCERT Solutions for CBSE Students
Question: We see the sun rising 8 1/4 minutes after it has risen. Why?
Answer: The speed of light is 3 lakh per second. The sun’s raise take time to reach on earth.
Question: Name two sources of light and two man-mad sources of light.
Answer:
- Man-mad source of light are: Tube light, candle.
- Source (natural) of light are: Sun, firefly.
Question: How do we see non-luminous objects?
Answer:
- Light should fall on the object.
- The object should reflect light towards our eyes.
Question: What is meant by ‘rectilinear propagation of light’?
Answer: It means that light always travel in straight line.
Question: When is a shadow formed?
Answer: When the source of light is blocked with opaque or translucent object that forms shadow.
Question: Why does a solar eclipse always occur on new moon day?
Answer: When the sun, moon and earth are in a line and moon blocks the light it is solar eclipse. But half of the moon receives light and the other does not receive the light. Hence, the moon is not visible on solar eclipse day.
Question: When can you see the image of an object in a plane mirror?
Answer:
- Light should fall on the object.
- Object should reflect the light.
- Mirror should reflect the light.
- And the reflected light should reach our eyes.
Question: List three properties of a shadow.
Answer:
- It is always on the angle at which the light falls.
- It always on the opposite source of light.
- It always shows the outline image and not the details of the image.
Question: In what ways is an image different from a shadow?
Answer: Shadow:
- When a shadow is formed it is completely black in colour.
- A shadow is similar in shape to the object but never shows the details of the object.
Image:
- When an image is formed the colour remains the same.
- An image is not only of the same shape of the object but shows all the details of object.
Question: Draw a diagram to show the formation of the image of a distance tree by a pinhole camera.
Answer:
