Electricity

21. Rectifiers convert ______ . [S.S.C. Online CHSL (T-1) 20.01.2017 (shift-I)]

(a) high voltage to low voltage
(b) low voltage to high voltage
(c) AC to DC
(d) DC to AC

Correct Answer: (c) AC to DC

Solution:A rectifier is an electrical device that converts alternating current (AC) into direct current (DC).

22. Rectifiers are used to convert_______ . [S.S.C Online Stenographer 14.09.2017 (Shift-I)]

(a) high voltage to low voltage
(b) low voltage to high voltage
(c) DC to AC
(d) AC to DC

Correct Answer: (d) AC to DC

Solution:A rectifier is an electrical device that converts alternating current (AC) into direct current (DC).

23. Which law of physics states that the force between the two electric charges reduces to a quarter of its former value when the distance between them is doubled? [S.S.C. Online Graduation Level (T-1) 3.03.2020 (Shift-II)]

(a) Pascal's Law
(b) Hooke's Law
(c) Stefan's Law
(d) Coulomb's Law

Correct Answer: (d) Coulomb's Law

Solution:

The law of physics that states that the force between the two electric charges reduces to a quarter of its former value when the distance between them is doubled is Coulomb's Law.

Coulomb's Law states that the electrostatic force between two point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between their centers. Mathematically, it is expressed as:

$F=k\frac{|q_1 q_2|}{r^2}\quad\;$ where:

(F) is the electrostatic force between the charges.
(k) is Coulomb's constant.
(q_1) and (q_2) are the magnitudes of the charges.
(r) is the distance between the centers of the two charges. $F'=k\frac{|q_1 q_2|}{(2r)^2}=k\frac{|q_1 q_2|}{4r^2}=\frac{1}{4}\left(k\frac{|q_1 q_2|}{r^2}\right)=\frac{1}{4}F$

This shows that when the distance between the two electric charges is doubled, the force between them reduces to one-quarter (a quarter) of its original value. This inverse square relationship is a key feature of Coulomb's Law.

24. Whose law states that at a junction in an electric circuit, the sum of the currents flowing into the junction is equal to the sum of the currents flowing out of the junction? [S.S.C. Online CPO SI (T-1) 10.11.2022 (Shift-II)]

(a) Michael Faraday
(b) Georg Simon Ohm
(c) Victor Francis Hess
(d) Gustav Robert Kirchhoff

Correct Answer: (d) Gustav Robert Kirchhoff

Solution:The law that states that at a junction in an electric circuit, the sum of the currents flowing into the junction is equal to the sum of the currents flowing out of the junction is called Kirchhoff's Current Law (KCL).

25. ________states that the ratio of the potential difference across a conductor to the current flowing through it is a constant, provided that its physical conditions, such as temperature, remain constant. [S.S.C. Online CHSL (T-1) 25.01.2017 (Shift-II)]

(a) Lenz's Law
(b) Hooke's Law
(c) Ohm's Law
(d) Coulomb's Law

Correct Answer: (c) Ohm's Law

Solution:According to Ohm's law, if there is no change in the physical state of a conductor, such as a temperature, then the value of the current flowing in the conductor is directly proportional to the potential difference across its ends. Therefore,

I α V
V α I
V = IR

Here the constant R is called the resistance of the conductor.

26. The value of the electric current flowing between the two end points of a conductor is proportional to the potential difference between them and is called- [C.P.O. 5.1.5.06.2016 (Shift-4)]

(a) Avogadro's Law
(b) Raoult's Law
(c) Ohm's Law
(d) Faraday's Law

Correct Answer: (c) Ohm's Law

Solution:According to Ohm's law, if there is no change in the physical state of a conductor, such as a temperature, then the value of the current flowing in the conductor is directly proportional to the potential difference across its ends. Therefore,

I α V
V α I
V = IR

Here the constant R is called the resistance of the conductor.

27. Coulomb per second is equivalent to_______ . [S.S.C. Online CGL (T-1) 24.08.2021 (Shift-I)]

(a) joule
(b) volt
(c) ohm
(d) ampere

Correct Answer: (d) ampere

Solution:Electric current is the rate of flow of charge in a circuit. Its unit is (coulomb/second).

1 (coulomb/second) = 1 ampere

Hence, (coulomb/second) represents ampere.

28. Transformer is a device to convert- [S.S.C. Online Graduation Level (T-1) 3.09.2016 (Shift-II)]

(a) D.C. to A.C.
(b) Low voltage D.C. into high voltage D.C.
(c) Low voltage A.C. into high voltage A.C.
(d) Mechanical energy into Electrical energy

Correct Answer: (c) Low voltage A.C. into high voltage A.C.

Solution:A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts.

It converts high voltage AC into low voltage AC and vice-versa.
It is based upon the principle of mutual induction.
Transformers alone cannot convert AC to DC or DC to AC; besides, they cannot change the voltage or current of DC.

29. A transformer can do all of the following except: [S.S.C. Online CHSL (T-1) 7.02.2017 (Shift-I)]

(a) step up a/c voltage
(b) step up a/c current
(c) step up a/c power
(d) step down a/c voltage

Correct Answer: (c) step up a/c power

Solution:A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.

It is widely used in electric power transmission and appliances to convert mains voltage to low voltage to power electronic devices.
It cannot step-up a/c power.

30. In Alternating Current, which of the following devices is used to easily and efficiently convert voltages from one voltage to another? [S.S.C. JE Civil Exam 30.10.2020 (Shift-I)]

(a) Transformer
(b) Resistor
(c) Inverter
(d) Rectifier

Correct Answer: (a) Transformer