# 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)