Electric Current (Physics) Part-II

Total Questions: 39

11. Small drops of the same size are charged to V volts each. If n such drops coalesce to form a single large drop, its potential will be: [U.P. Lower Sub. (Mains) 2015]

Correct Answer: (a) n⅔ V
Solution:

12. Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R). [I.A.S. (Pre) 1996]

Assertion (A): Transformer is useful for stepping up or stepping down voltages.

Reason (R) : Transformer is a device used in D.C circuits.

In the context of the above two statements, which one of the following is correct?

Correct Answer: (c) (A) is true but (R) is false
Solution:

A transformer transfers electric energy between two or more interconnected circuits through electric induction. It converts the high voltage to low voltage and low voltage to high and transmits it.

Transformers can only function with alternating current (AC) not with direct current (DC).

13. Transformer is used for: [U.P.P.C.S. (Pre) 2006]

Correct Answer: (d) To step-up or step-down AC voltages
Solution:

The transformer is used to step-up and step-down the alternating current. There are two types of coils in transformers (i) Primary coil (2) Secondary coil. Alternating current flows through the primary coil which inflicts the potential in the secondary coil.

14. Which of the following is the purpose for which a transformer is used? [U.P.P.C.S. (Mains) 2011]

Correct Answer: (c) To step-up or step-down AC voltage
Solution:

The transformer is used to step-up and step-down the alternating current. There are two types of coils in transformers (i) Primary coil (2) Secondary coil. Alternating current flows through the primary coil which inflicts the potential in the secondary coil.

15. A mobile phone charger is: [U.P.P.C.S. (Pre) 2017]

Correct Answer: (d) A step down transformer
Solution:

A mobile phone charger works on the simple principle of conversion of AC (alternating current) to DC (direct current). As we connect charger to 220 volt AC switchboard, the first job of the charger is to step down the high 220 v in 9 v or 10 v. A step down transformer is used in mobile phone charger.

16. Some pairs of devices and associated energy changes are given below: [R.A.S./R.T.S.(Pre) 2013]

(i) Electric generator - Mechanical to electrical

(ii) Electric motor - Electrical to mechanical

(iii) Diesel engine - Light to electrical

(iv) Solar cell - Chemical to mechanical

Which of the above pair/s is/are correctly matched?

Correct Answer: (a) (i) and (ii)
Solution:

An electric generator is a device that converts mechanical energy obtained from an external source into electrical energy as the output. A motor converts electrical energy to mechanical energy.

A diesel engine is an internal-combustion engine in which heat produced by the compression of air in the cylinder is used to ignite the fuel. Solar (or photovoltaic) cells convert the sun's energy into electricity.

17. An AC current can be produced by: [69ᵗʰ B.P.S.C. (Pre) 2023]

Correct Answer: (b) dynamo
Solution:

Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction.

An AC current is produced by a dynamo which is called AC dynamo or alternator. This is done by rotating a coil or armature within the magnetic field created by field coils.

If a DC current is required it can be supplied by a commutator in a DC dynamo. It is important to note that the current produced by a simple dynamo is alternating current (AC), as the direction of the current changes with each half turn of the coil.

However, generally dynamos incorporate a component called a commutator, which converts the AC into direct current (DC).

18. The basic difference between an AC generator and a DC generator is that- [Chhattisgarh P.C.S. (Pre) 2018]

Correct Answer: (b) AC generator has slip rings while the DC generator has a commutator
Solution:

The rotating armature of an AC generator is connected to an external circuit by the means of slip rings. In a DC generator, the commutator is used to reverse the directions of the natural alternating voltage every half cycle.

So AC generator has slip rings while DC generator has a commutator.

19. Alternate current is not preferable- [R.A.S/R.T.S. (Pre) 1994]

Correct Answer: (a) To charge storage battery
Solution:

Direct Current is used to charging the batteries with the help of rectifier which converts AC to DC. Thus alternate current is not preferable for it.

20. The device used for converting alternating current to direct current is called- [Chhattisgarh P.C.S. (Pre) 2008, U.P.P.C.S. (Pre) 2006]

Correct Answer: (b) Rectifier
Solution:

Rectifier is an electric device that converts alternating current (AC) to direct current (DC).

Inverter is an electronic circuit that changes direct current (DC) to Alternating Current (AC).

The transformer supply alternating current or electric power from power grid to those appliances which use different voltages.

Transmitter is an electronic device which, with the aid of antenna produces electromagnetic signals/radio waves. Primarily it is used for radio, television and in other communication tools.