Electricity — Science STD 10 — Question

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

The near point of the eye of a person is 50cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25cm. from the eye.

Draw a diagram to show how a converging lens held close to the eye acts as a magnifying glass. Why is it usual to choose a lens of short focal length for this purpose rather than one of long focal length?

How are we able to see nearby and also the distant objects clearly?

An image formed on a screen is three times the size of the object. The object and screen are 80cm apart when the image is sharply focussed.

1. State which type of lens is used.
2. Calculate focal length of the lens.

Differentiate between a glass slab and a glass prism. What happens when a narrow beam of:

1. A monochromatic light.
2. White light passes through.

1. Glass slab.
2. Glass prism?

Give the position, size and nature of image formed by a concave lens when the object is placed:

1. Anywhere between optical centre and infinity.
2. At infinit.

In 10s, a charge of 25C leaves a battery, and 200j of energy are delivered to an outside circuit as a result.

1. What is the p.d. across the battery?
2. What current flows from the battery?

The magnification of an image formed by a lens is – 1. If the distance of the image from the optical centre of the lens is 35 cm, where is the object placed ? What is the nature and focal length of the lens? If the object is displaced 20 cm towards the optical centre of the lens, where would the image be formed and what will be its nature? Draw a ray diagram to justify your answer.