A small brass sphere having a positive charge of 1 .7 × 10 − 8 C is made to touch another sphere of the same radius having a negative charge of 3 .0 × 10 − 9 C . Find the force between them when they are separated by a distance of 20 cm . What will be the force between them when they are immersed in an oil of dielectric constant 3 ?

When the charges are brought in contact charges on them becomes equal as the radii of the spheres are equal. Charge on each sphere q = 17 × 10 − 9 + − 3 .0 × 10 − 9 2 C = 7 × 10 − 9 C Separation r = 20 cm = 20 × 10 − 2 m Dielectric constant k = 3 From coulombs law, Force between them when they are placed in air F = 1 4 πε ∘ q 1 q 2 r 2 ⇒ F = 9 × 10 9 × 7 × 10 − 9 × 7 × 10 − 9 20 × 10 − 2 2 ⇒ F = 1 .1 × 10 − 5 N Force between the spheres when placed in air is 1 .1 × 10 − 5 N The force between them when they are placed in the oil of dielectric 3 is F = 1 4 πε ∘ k q 1 q 2 r 2 ⇒ F = 9 × 10 9 3 × 7 × 10 − 9 × 7 × 10 − 9 20 × 10 − 2 2 ⇒ F = 0 .37 × 10 − 5 N Force between the spheres when immersed in oil is 0 .37 × 10 − 5 N

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12th CBSE

IMPORTANT

Earn 100

The distance between the electron and proton in hydrogen atom is $5 .3 \times 10^{- 11} m$ . Determine the magnitude of the ratio of electrostatic and gravitational force between them.

Given $m_{e} = 9 .1 \times 10^{- 31} kg$ , $m_{p} = 1 .67 \times 10^{- 27} kg$ , $e = 1 .6 \times 10^{- 19} C$ and $G = 6 .67 \times 10^{- 11} {Nm}^{2} {kg}^{- 2}$ .

Important Questions on Electric Charges and Field

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12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 8

Two identical metallic spheres, having unequal opposite charges are placed at a distance

0.90 m

apart in air. After bringing them in contact with each other, they are again placed at the same distance apart. Now the force of repulsion between them is

0.025 N

. Calculate the final charge on each of them.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 9

A small brass sphere having a positive charge of

1 .7 \times 10^{- 8} C

is made to touch another sphere of the same radius having a negative charge of

3 .0 \times 10^{- 9} C

. Find the force between them when they are separated by a distance of

20 cm

. What will be the force between them when they are immersed in an oil of dielectric constant

3

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 10

The sum of two point charges is

7 μ C

. They repel each other with a force of

1 N

when kept

30 cm

apart in free space. Calculate the value of each charge.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 11

Two point charges

q_{1} = 5 \times 10^{- 6} C

and

q_{2} = 3 \times 10^{- 6} C

are located at positions

(1 m, 3 m, 2 m)

and

(3 m, 5 m, 1 m)

respectively. Find the forces

{\vec{F}}_{12}

and

{\vec{F}}_{21}

using vector form of Coulomb’s law.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 12

Three equally charged small objects are placed as shown in fig 1.18. The object $A$ exerts an electric force on object $B$ equal to $3 .0 \times 10^{- 6} N$ .

Question Image

What electric force does $C$ exert on $B$ ?

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 12

Three equally charged small objects are placed as shown in fig 1.18. The object $A$ exerts an electric force on object $B$ equal to $3 .0 \times 10^{- 6} N$ .

Question Image

What is the net electric force on $B$ ?

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 13

Two identical metallic spheres

A

and

B

, each carrying a charge

q

, repel each other with a force

F

. A third metallic sphere C of the same size, but uncharged, is successively made to touch the spheres

A

and

B

, and then removed away. What is the force of repulsion between

A

and

B

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Problems For Practice>Q 14

Two point charges

+ 9 e

and

+ e

are kept at a distance

a

from each-other. Where should we place a third charge

q

on the line joining the two charges so that it may be in equilibrium?

The distance between the electron and proton in hydrogen atom is 5.3×10−11m. Determine the magnitude of the ratio of electrostatic and gravitational force between them. Given me=9.1×10−31kg, mp=1.67×10−27kg, e=1.6×10−19C and G=6.67×10−11Nm2kg−2.

Important Questions on Electric Charges and Field

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