# Electrical Circuit – Short Questions Collection With Answer | Physics Class 12

## Very Important Questions Collection HSEB | Science Faculty Electrical Circuit – Physics Grade XII Short Questions with Answer (Solution)

1. State Kirchhoff’s laws in electricity.
Ans. There are two Kirchhoff’s laws in electricity. They are :

(a) Kirchhoff’s current law (KCL) : It states that the algebraic of the currents meeting at a junction in an electrical circuit is always zero. It means the sum of current flowing towards any junction in an electrical circuit is equal to the sum of currents flowing away from that junction. This law is also termed as the junction law.This law is based on the principle of conservation of charge.

(b) Kirchhoff’s voltage law (KVL) : It state that, in any closed electrical circuit, the algebraic sum of all emfs is always equals to the algebraic sum of voltage drops in resistors.This law is also called loop law.This law is based on the principle of conservation of energy.

2. Why is wheat- stone Bridge not suitable for measuring very low resistance?
Ans. When all the four resistance are nearly equal, the sensitivity of wheat-stone Bridge is very high. It means that to measure a very low resistance, the resistance of other resisters should be used , which itself would be insensitive and it will introduce error in measurement. That’s why, a wheat-stone bridge is not suitable for measuring very low resistance.

3. For making the wheat-stone Bridge most sensitive, how it should be arranged?
Ans. For making the wheat-stone bridge most sensitive, all the four resistance and the galvanometer resistance must be of the same order.

4. “Wheat-stone bridge is not suitable for measuring high resistance .” why?
Ans. Wheat-stone bridge is not suitable for measuring high resistance because a galvanometer having high resistance must be used for measuring high resistance . In that case, the current through the galvanometer will be low and it will become insensitive.

5. What is meter Bridge ?
Ans. A sensitive device, which is used to measure the unknown resistance, is called Meter Bridge.It is based on the principle of stone bridge. The value of unknown resistance X can be measured by using the relation,

`X = 100 - I/I x R, where I is the balancing length at null deflection for resistance R.`

6. What is potentiometer? Write its working principle also.
Ans.  A device, which is used to measure the e.m.f. of a cell or p.d. between two points of an electric circuit, is called a potentiometer.
` Principle : Since, V=IR and R= p I/A => V = Ip I/A For constant I, p and A, we get, V α I `
i.e. if a wire of uniform cross sectional area is carrying a steady current, then fail of potential across any portion of the wire is directly proportional to the length of that portion . This is the working principle of potentiometer.

7. What do you mean by potentiometer wire is uniform. why?
Ans.  The potential difference per unit length of the wire of a potentiometer is called its potential gradient. Smaller the potential gradient, better its sensitivity.

8. What are the advantage of a potentiometer over voltmeter?
Ans. A potentiometer is preferred to a voltmeter for two reasons :

(a) When a voltmeter is used to measure the e.m.f. of a cell it will not give the correct value of e.m.f., because it will draw some current from the cell. The circuit is not open and the reading shown by the voltmeter will be the terminal potential difference, e.m.f.

On the other hand, if e.m.f. is measured by a potentiometer, the galvanometer shows null deflection in which case no current is drawn from the cell and the cell is in open circuit. As, a result, the corresponding voltage will be the e.m.f. Therefore , we can say that a potentiometer is equivalent to an ideal voltmeter of infinite resistance.

(b) While taking reading with a voltmeter, deflection of the needle is read, whereas with potentiometer null deflection is taken.Therefore, error in the measurement with voltmeter will be larger than with a potentiometer.

9. A potentiometer can be taken as taken as voltmeter of infinite resistance.Explain.
Ans. When the e.m.f. of a cell is measured by a potentiometer, the current flowing through the galvanometer is zero.Consequently, the actual value of e.m.f. of the cell be measured . If the above condition is to be realized with a voltmeter, it should have infinite resistance. that’s why; a potentiometer is taken as a voltmeter of infinite resistance.

10.What is the advantage of using a greater length of potentiometer wire?
Ans. The sensitivity of the potentiometer can increased by using a greater length of the potentiometer wire. The greater the length of the potentiometer gradient along the wire. Hence, the distance of the null position will be increased which can be measured more accurately.

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