# Important Short Questions | Physics | Class 12 | Electrostatic (Chapter 1) | 2020 Board Exams (CBSE)

SUBJECT – SCIENCE (PHYSICS)
CLASSXII (12th)
QUESTIONS FROM – CHAPTER 1 (ELECTROSTATIC)
IMPORTANT QUESTION ANSWERS FOR BOARD EXAMS 2020 !
Important Short Questions | Physics | Class 12 | Electrostatic (Chapter 1) | 2020 Board Exams (CBSE)

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Q1. What do you mean by surface charge density? Write S.I unit?
Answer – The charge per unit area of surface is known as surface charge density. If a charge Q be uniformly distributed in an area A of surface, the surface charge density σ is given by,
σ = Q/A.
The S.I unit of the surface charge density is “coulomb per square metre”.

Q2. What is the main practical purpose of the capacitor?
Answer – To hold more charge at smaller potential difference so that charge could not leak out due to dielectric breakdown.
For example – In a parallel plate capacitor, V <= E max. d which means Q <= C E max. d. For large C, we can hold large Q.

Q3. Write two basic properties of electric charge?

Answer – Two basic properties of electric charge are :-
(i) Quantization of electric charge,
(ii) Conservation of electric charge,
Any charge that can be transferred to a body is integral multiple of elementary charge :- Q = ne, where +- n = 1,2,3….

e = 1.6 x 10 (-19) C

Q4. Write the significance of representation of Coulomb’s law in vector form?
Answer – Coulomb law in vector form is more informative than is scalar form. So the main reasons are as follows :-

(I) It is clear indicates that f12 and f21 are equal in magnitude but have opposite direction.

(II) it indicates that Coulomb force is a central force either X along the line joining the two charges.

Q5. Define electric dipole moment and write its S.I unit?
Answer – The vector sum of the product position vector with point charges is known as dipole moment of a charge distribution about the origin.

For two opposite point charges it is directed from negative to positive charge and equals the product of charge and separation. S.I unit of electric dipole moment is coulomb metre.

Q6. State and explain superposition principle for electric fields.
Answer – Each charge produces its own field as if other charges were not present. The net field is vector sum of individual fields.

At point p the fields are added to give the net field.
E = E1+E2+E3….

Q7. What is law of conservation of charge?
Answer – Charges and neither created nor destroyed. There is transfer of charge. Total system remains conserved -production.

Q8. What are the significance of electric lines of force?
Answer – These lines are used to represent electric field due to a point charge or system of the point charge. It remarkable that these lines are imaginary. they are originated from positive charge and enters the negative charge. The dense population indicates strong electric field and real populate indicates weak field.

Q9. What do you mean by electric flux?
Answer – If an electric field an elementary area is considered parallel to the direction electric field intensity then a each point of this area is E uniform and the product of magnitude of intensity (E) and area ds is called electric flux associated with that area.

The SI unit is voltmeter and it is a scalar quantity.

Q10. Define electric field intensity and also write its S.I unit and Dimensional formulae?
Answer – Electric field intensity at a point in an electric field is electric force per unit test charge placed at a point. If a test charge Q<not> experiences a force F when placed at rest at the point, the force per unit test charge E given by,

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