Reflection of Light — Science STD 10 — Question

100 joules of heat is produced per second in a 4 ohm resistor. What is the potential difference across the resistor?

An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.

If you walk from a dark room into sunlight and back again into dark room, how would your pupils alter in size? What makes this happen?

When an object is placed at a distance of 36cm from a convex lens, an image of the same size as the object is formed. What will be the nature of image formed when the object is placed at a distance of:

1. 10cm from the lens?
2. 20cm from the lens?

Explain with a suitable diagram, how a concave mirror converges a parallel beam of light rays. Mark clearly the pole, focus and centre of curvature of concave mirror in this diagram.

What is the potential difference between the terminals of a battery if 250 joules of work is required to transfer 20 coulombs of charge from one terminal of battery to the other?

Write some of the important uses of electromagnets.

Write a low resistance device name which is always connected in series with the device through which the current is to be measured.

An object of height 2.5cm is placed at a distance of 15cm from the optical centre ‘O' of a convex lens of focal length 10cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O', principal focus F and height of the image on the diagram.

A person can read a book clearly only if he holds it at an arm's length from him. Name the defect of vision:

1. If the person is an old man.
2. If the person is a young man.