Magnetic Effects of Electric Current — Science STD 10 — Question

How does the resistance of a wire vary with its:

1. Area of cross-section?
2. Diameter?

An object is placed at a distance of 30cm in front of a convex mirror of focal length 15cm. Write four characteristics of the image formed by the mirror.

Explain why, the current that makes the heater element very hot, only slightly warms the connecting wires leading to the heater.

Your friend can read a book perfectly well but cannot read the writing on blackboard unless she sits on the front row in class.

1. Is she short-sighted or long-sighted?
2. What type of lenses-converging or diverging-would an optician prescribe for her?

Refractive indices of four mediaA, B, CandDare given below:

Medium	Refractive index
A B C D	1.33 1.44 1.52 1.65

In which of these four media is the speed of light:

1. Maximum, and
2. Minimum?

Draw ray diagrams showing the image formation by a concave lens when an object is placed:
At the focus of the lens.

“The magnification produced by a spherical mirror is - 3”. List four informations you obtain from this statement about the mirror/ image.

Why is an electric light bulb not filled with air? Explain why argon or nitrogen is filled in an electric bulb.

An object is placed just outside the principal focus of concave mirror. Draw a ray diagram to show how the image is formed, and describe its size, position and nature.

Write one use of wind energy.

1. In the past.
2. At present.