A charge is a property associated with the matter due to which it experiences and produces an electric and magnetic field.

- Charges are scalar in nature and they add up like real numbers. (Additivity of Charges)
- The total charge of an isolated system is always conserved. ( Conservation of Charge)
- Charges exist in a discrete amount rather than continuous value. Hence, quantised. (Quantisation of Charge)

**Question and Answer**

1. Pick the correct statement

- The glass rod gives protons to silk when they are rubbed against each other.
- The glass rod gives electrons to silk when they are rubbed against each other.
- The glass rod gains protons from silk when they are rubbed against each other.
- The glass rod gains electrons when they are rubbed against each other.

**Answer: (b)Â **The glass rod gives electrons to silk when they are rubbed against each other.

2. A force F acts between two charges +Q and -Q that is placed at a certain distance from each other. The third sphere of charge Q is placed between them. What is the magnitude and force experienced by the third charge?

- 3F in the direction of +Q charge
- 4F in the direction of +Q charge
- 8F in the direction of -Q charge
- No direction and magnitude is zero

**Answer: **(c) 8F towards -Q charge

3. At the four corners of the square A, B, C and D, Four charges of equal magnitude q are placed. Determine the magnitude of the force acting on the charge at point B?

- \(\frac{(\frac{2+1}{\sqrt{2}})q^2}{4\pi \varepsilon _0a^2}\)
- \(\frac{(1+2\sqrt{2})q^2}{2\times 4\pi \epsilon _0a^2}\)
- \(\frac{4q^2}{4\pi \epsilon _0a^2}\)
- \(\frac{3q^2}{4\pi \epsilon _0a^2}\)

**Answer: **(b) \(\frac{(1+2\sqrt{2})q^2}{2\times 4\pi \epsilon _0a^2}\)

4. At a distance r, two equal charges are kept and they exert a force F on each other. What is the force acting on each charge, if the distance between them is doubled and charges are halved?

- F/4
- 4 F
- F/16
- F/8

**Answer: **(c) F/16

5. Determine the total electric flux of a unit positive charge which is kept in the air?

- \({\epsilon _0}^{-1}\)
- \({\epsilon _0}\)
- \(4\pi \epsilon _0\)
- \({4\pi \epsilon _0}^{-1}\)

**Answer: **(d) \({4\pi \epsilon _0}^{-1}\)

6. The variation of electric field E due to a hollow spherical conductor of radius R as a function of distance from the centre of the sphere is shown in which of the following graphs?

** Answer:** (b)

7. Pick the correct statement from the following

- If the point has a charge then the electric field is discontinuous at the point.
- Continous electric field at a point
- Continous electric field at a point if a charge is present at the point.
- At the point, the electric field is discontinuous if a negative charge is present at the point.

**Answer:** (a)Â If the point has a charge then the electric field is discontinuous at the point.

8. When is Gauss law true?

- the speed of light isn’t a universal constant
- the inverse square law is false
- magnetic monopoles are present
- None of the above

**Answer: **(b) the inverse square law is false

9. What is the SI unit of permittivity of free space?

- Weber
- Farad
- C
^{2}N^{-1}m^{-2} - C
^{2}N^{-1}m^{2}

**Answer: **(c) C^{2}N^{-1}m^{-2}

10. Pick the true statements about electric field lines

- It provides information about the direction of the electric field
- Electric field lines provide information about the type of charge
- Electric field lines provide information about the field strength
- All of the above

**Answer: **(d) All of the above

11. The electric field lines due to a single negative charge are represented by

**Answer: **(b)

12. Which surface is considered for Gauss law?

- Spherical surface
- Closed Surface
- Gaussian Surface
- Plane Surface

**Answer:** (c) Gaussian Surface

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