Human Eye and Colourful World — Science STD 10 — Question

A student determines the focal length of a device ‘X’ by focusing the image of a distant object on a screen placed 20cm from the device on the same side as the object. The device ‘X’ is.

A TV set consumes an electric power of 230 watts and runs on 230 volts mains supply. The correct fuse for this TV set is:

1. 5A
2. 3A
3. 1A
4. 2A

A horizontal wire carries a current as shown in Figure below between magnetic poles N and S:

Is the direction of the force on the wire due to the magnet:

The resistivity of copper metal depends on only one of the following factors. This factor is:

1. Length.
2. Thickness.
3. Temperature.
4. Area of cross-section.

In a convex spherical mirror, reflection of light takes place at:

A student is using a convex lens of focal length 10 cm to study the image formation by a convex lens for the various positions of the object. In one of his observations, he may observe that when the object is placed at a distance of 20 cm from the lens, its image is formed at (select the correct option):

A teacher sets up the stand carrying a convex lens of focal length 15 cm at 42.7 cm mark on the optical bench. He asks four students A, B, C and D to suggest the position of screen on the optical bench so that a distinct image of a distant tree is obtained almost immediately on it. The positions suggested by the students were as:

1. 12.7 cm.
2. 29.7 cm.
3. 57.7 cm.
4. 72.7 cm.

The correct position of the screen was suggested by.

The most suitable material for making the core of an electromagnet is:

1. Soft iron.
2. Brass.
3. Aluminium.
4. Steel.

A virtual, erect and magnified image of an object is to be produced with a concave mirror of focal length 12cm. Which of the following object distance should be chosen for this purpose?