# Physics Questions and Answers – Electric Charges

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Electric Charges”.

1. The attraction is the real proof of an object being charged.
a) True
b) False

Explanation: If an object is attracted by another charged body, the first object may be oppositely charged or not charged because we know both an uncharged object and an oppositely charged object are attracted by another charged object.

2. If an object is positively charged, theoretically the mass of the object ______
a) Increases slightly by a factor of 9.11*10-31 kg
b) Decreases slightly by a factor of 9.11*10-31 kg
c) Remains the same
d) May increase or decrease

Explanation: If an object is positively charged it loses some of its electrons. The mass of an electron is 9.11*10-31 kg. So, if a positively charged body loses ‘n’ number of electrons, it mass decrease by the amount n*9.11E-31kg.

3. Why is gold used in the Gold-leaf electroscope?
a) Gold is easily available in nature
b) Gold is malleable
c) Gold is conducting in nature
d) Gold is cheap

Explanation: Though gold is a costly metal it is used in electroscope because of the property malleability. This means very thin and light sheets can be formed from gold simply by hammering or rolling and hence the deflection of the light gold plates increases.
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4. What happens to the plates of the apparatus if we measure alternating charge using a Gold-leaf oscilloscope?
a) It doesn’t diverge at all
b) It diverges momentarily
c) The plates give a proper divergence
d) The degree of divergence increases and decreases repeatedly

Explanation: The divergence of the plates of the Gold-leaf oscilloscope depends only on the presence of a charge, not on the quality of charge i.e. positive or negative. So, if the charge changes from positive to negative and vice versa the degree of divergence of the plates remains the same.

5. Which one of the following is the correct diagram of charge distribution in a hollow sphere?
a)

b)

c)

d)

Explanation: The same charges repel each other. So, they try to maintain maximum distance from each other and hence they try to remain at the outer surface of an object. If the charge remains on the inner surface or throughout the body, they will repel each other with greater force.

6. Dr. Gilbert tried to hold a brass rod by hand and induce static electricity in it by friction. Why did he fail?
a) Static electricity is induced only on insulators while brass is conducting
b) The induced static charge flew through his hand and body to the ground
c) The static charge was not produced at all
d) It is not possible to induce static electricity by friction

Explanation: The human body is a good conductor and hence the charge produced by friction flew through his body to the ground. We can tackle the problem simply by holding the brass rod with the help of some insulated holder.

7. Gold-leaf electroscope can be used _______
a) Only to detect the presence of charge
b) To detect the presence of charge as well as its nature (positive or negative)
c) To measure the surface charge density
d) To measure current

Explanation: If the apparatus is initially in contact with some positively charged body and then comes in contact with another charged body and if the divergence increases we can deduce that the second body is also positively charged. If the divergence decreases then the second body must be negatively charged.

8. When a glass rod is rubbed with silk, what kind of charge will be developed on glass?
a)

b)

c)

d) Cannot predict

Explanation: According to electrostatic series, glass is situated above silk. So, if the glass is rubbed with silk, the positive charge on glass and negative charge on silk is produced. Similarly, we can predict what is the nature of charge if we rub two di-electric substances together.

9. 1 Coulomb = ________ Electro Static Unit.
a) 3*109
b) 3*108
c) 1.602*10-19
d) 2*109

Explanation: 1 Coulomb means 3*109 Electro Static Unit of charge. Coulomb and ESU are two different units of charge and their conversion formula is necessary. Coulomb is the unit of charge in the SI system and esu is the unit of charge in the CGS system.

10. Number of electrons in 1 Coulomb charge is _________
a) 6.25*1021
b) 6.25*1020
c) 6.25*1025
d) 6.25*1023

Explanation: Electron has the charge of 1.602*10-19 Coulomb. So, the number of electrons in 1 Coulomb of charge is $$\frac{1}{1.602*10^{-19}}$$ = 6.25*1021. This huge number of electrons can be accumulated to form 1C of charge. Thus, we can conclude that we need Avogadro’s number of electrons (approximately) to get 100C charges.

11. Two equally charged spheres attract each other. Now if they touch each other then they will _____
a) Attract each other with the same amount of force
b) Repel each other
c) Attract each other with less amount of force
d) Don’t attract or repel

Explanation: The two spheres are oppositely charged by the same amount. So if they come in contact, both of their charges are neutralized. So they become uncharged and don’t attract or repel each other.

12. Which among the following cannot be the charge of a charged body?
a) 4.8*10-14 Coulomb
b) 6.4*10-15 Coulomb
c) 5*10-14 Coulomb
d) 3.2*10-10 Coulomb

Explanation: Charge of a body must be an integral multiple of charge of an electron. 5*10-14 is not an integral multiple of (1.602*10-19 Coulomb) which is equal to the charge of an electron. But we can see that 4.8, 6.4, 3.2 are integral multiples of 1.6.

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