NCERT Science Class 10 Chapter 16 Electricity CBSE Board Sample Problems Very Short Answer

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Question

Why is tungsten metal used in bulbs but not in fuse wires?

Solution

• ANS-It is because tungsten has a very high melting point.

• If it is used as a fuse wire, then it will not melt even when large amount of current is passed through it, and the appliance will be damaged

Question

Why are copper wires used as connecting wires?

Solution

The electrical resistivity of copper is low.

Question

(1)By what other name is the unit joule/coulomb called?

Solution

Volt

Question

Nichrome is used to make the element of an electric heater why?

Solution

Nichrome is an alloy of high resistivity and high melting point and does not oxidise easily

Question

Name the instrument used to measure

(i) Electric current in a circuit,

(ii) Potential difference between two points in a circuit

Solution

(i) Ammeter,

(ii) Voltmeter

Question

State Ohm’s Law

Solution

According to Ohm’s Law at constant temperature and pressure, the current passing through a conductor is directly proportional to the potential difference across its end, i.e.

Question

When do we say that the potential difference between two points of a circuit in 1 voIt

Solution

Potential difference between two points of an electric circuit is said to be 1 volt when a work of 1 J is to be done for moving a charge of 1 C between two points.

Question

What happens to the resistance of a conductor when temperature is increased?

Solution

The resistance of a conductor increase with rise in temperature. As R ci T.

Question

Why is tungsten used for making filament of electrical bulbs?

Solution

Because tungsten has high melting point and high (resistivity).

Question

Why do we prefer using copper and aluminium for transmission of electric current?

Solution

Because of their low resistivity /cost.

Question

Two bulbs having power of 50 w and 25 w respectively are connected with the same source. Which has higher resistance?

What is their ratio?

Solution

¡e, 50 W bulb has ½ resistance than 25 W.

Question

A wire of resistance 5 is bent in the form of a closed circle.

Find the resistance across the diameter of the circle?

Solution

R=5

Consider two semicircular elements connected across the diameter.

Total resistance is 5

Resistance of two semicircular elements is

Both the elements are connected in parallel.

Question

List any two factors on which resistance of a wire depends on.

Solution

Resistance depends on:

Length of wire (directly proportional)

Cross-sectional area (inversely proportional)

Question

The electric power consumed by a device may be calculated by either of the two expressions or . the first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in these expressions be explained? (1)

Solution

is used to calculate electric power when the current flowing through the circuit is constant (Series combination).

(1/2)

is used to calculate electric power when the potential difference flowing through the circuit is constant (Parallel combination). (1/2)