Human Eye and Colourful World — Science STD 10 — Question

All appliances in a domestic electric circuit are connected in parallel so that:

A person cannot see distinctly objects kept beyond 2m. This defect can be corrected by using a lens of power:

1. +0.5D
2. -0.5D
3. +0.2D
4. -0.2D

Whatever be the position of the object, the image formed by a mirror is virtual, erect and smaller than the object. The mirror then must be:

1. Plane.
2. Concave.
3. Convex.
4. Either concave or convex.

The atmospheric refraction of light causes the twinkling of:

An object is placed at the following distances from a concave mirror of focal length 15cm, turn by turn:

1. 35cm
2. 30cm
3. 20cm
4. 10cm

Which position of the object will produce:

1. A magnified real image?
2. A magnified virtual image?
3. A diminished real image?
4. An image of same size as the object?

An electric heater is rated at 2kW. Electrical energy costs Rs 4 per kWh. What is the cost of using the heater for 3 hours?

The device used for producing electric current is called a:

An electric heater is rated at 2kW. Electrical energy costs Rs 4 per kWh. What is the cost of using the heater for 3 hours?

1. Rs 12.
2. Rs 24.
3. Rs 36.
4. Rs 48.

A student focused the image of a distant object using a device ‘X’ on a while screen ‘S’ as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device.

The lamps in a house hold circuit are connected in parallel because:

1. This way they required less current.
2. If one lamp fails the others remain lit.
3. This way they require less power.
4. If one lamp fails the other also fail.