This page focuses on the detailed Electric Charges and Field question answers for Class 12 Physics Electric Charges and Field, addressing the question: 'What is the force between two small charged spheres having charges of 2 x 10-7 C and 3 x 10-7 C placed 30 cm apart in air?'. The solution provides a thorough breakdown of the question, highlighting key concepts and approaches to arrive at the correct answer. This easy-to-understand explanation will help students develop better problem-solving skills, reinforcing their understanding of the chapter and aiding in exam preparation.

Question 1

What is the force between two small charged spheres having charges of 2 x 10^{-7} C and 3 x 10^{-7} C placed 30 cm apart in air?

Answer

Repulsive force of magnitude 6 × 10^{ - 3} N

Charge on the first sphere, q_{1} = 2 × 10 ^{- 7 }C

Charge on the second sphere, q_{2} = 3 × 10^{ - 7} C

Distance between the spheres, r = 30 cm = 0.3 m

Electrostatic force between the spheres is given by the relation,

Where, ∈_{0} = Permittivity of free space

Hence, force between the two small charged spheres is 6 × 10^{ - 3} N. The charges are of same nature. Hence, force between them will be repulsive.

- Q:-
An infinite line charge produces a field of 9 × 10

^{4}N/C at a distance of 2 cm. Calculate the linear charge density. - Q:-
A polythene piece rubbed with wool is found to have a negative charge of 3 × 10

^{−7}C.(a) Estimate the number of electrons transferred (from which to which?)

(b) Is there a transfer of mass from wool to polythene?

- Q:-
A 600 pF capacitor is charged by a 200 V supply. It is then disconnected from the supply and is connected to another uncharged 600 pF capacitor. How much electrostatic energy is lost in the process?

- Q:-
A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10

^{-12}F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6? - Q:- A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?
- Q:-
A regular hexagon of side 10 cm has a charge 5 µC at each of its vertices. Calculate the potential at the centre of the hexagon.

- Q:-
A point charge +10 μC is a distance 5 cm directly above the centre of a square of side 10 cm, as shown in Fig. 1.34. What is the magnitude of the electric flux through the square? (Hint: Think of the square as one face of a cube with edge 10 cm.)

- Q:-
A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is 1.5 × 10

^{3}N/C and points radially inward, what is the net charge on the sphere? - Q:-
A point charge of 2.0 μC is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?

- Q:-
The electrostatic force on a small sphere of charge 0.4 μC due to another small sphere of charge − 0.8 μC in air is 0.2 N.

(a) What is the distance between the two spheres?

(b) What is the force on the second sphere due to the first?

- Q:-
If the solenoid in Exercise 5.5 is free to turn about the vertical direction and a uniform horizontal magnetic field of 0.25 T is applied, what is the magnitude of torque on the solenoid when its axis makes an angle of 30° with the direction of applied field?

- Q:-
Four point charges q

_{A}= 2 μC, q_{B}= −5 μC, q_{C}= 2 μC, and qD = −5 μC are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square? - Q:-
Determine the current drawn from a 12 V supply with internal resistance 0.5 Ω by the infinite network shown in Fig. 3.32. Each resistor has 1 Ω resistance.

- Q:-
A spherical capacitor consists of two concentric spherical conductors, held in position by suitable insulating supports (Figure). Show

that the capacitance of a spherical capacitor is given by

where

*r*1 and*r*2 are the radii of outer and inner spheres, respectively. - Q:-
The work function of caesium metal is 2.14 eV. When light of frequency 6 ×10

^{14}Hz is incident on the metal surface, photoemission of electrons occurs. What is the(a) maximum kinetic energy of the emitted electrons,

(b) Stopping potential, and

(c) maximum speed of the emitted photoelectrons?

- Q:-
**Let us list some of the factors, which could possibly influence the speed of wave propagation:**(i) Nature of the source.

(ii) Direction of propagation.

(iii) Motion of the source and/or observer.

(iv) Wave length.

(v) Intensity of the wave.

**On which of these factors, if any, does**(a) The speed of light in vacuum,

(b) The speed of light in a medium (say, glass or water), depend?

- Q:-
A circular coil of 20 turns and radius 10 cm is placed in a uniform magnetic field of 0.10 T normal to the plane of the coil. If the current in the coil is 5.0 A, what is the

(a) total torque on the coil,

(b) total force on the coil,

(c) average force on each electron in the coil due to the magnetic field?

(The coil is made of copper wire of cross-sectional area 10

^{-5}m^{2}, and the free electron density in copper is given to be about 10^{29}m^{-3}.) - Q:-
A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10

^{-12}F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6? - Q:-
Digital signals

(i) Do not provide a continuous set of values,

(ii) Represent values as discrete steps,

(iii) Can utilize binary system, and

(iv) Can utilize decimal as well as binary systems.

Which of the above statements are true?

(a) (i) and (ii) only

(b) (ii) and (iii) only

(c) (i), (ii) and (iii) but not (iv)

(d) All of (i), (ii), (iii) and (iv).

- Q:-
Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW.

(a) Find the energy and momentum of each photon in the light beam,

(b) How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area), and

(c) How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?

Shubham Mishra
2019-10-17 20:37:48

Super ,pure phyisics ka video hai toh mere ko link bhejein

Lalisa
2019-08-19 21:06:15

Very nice

Gayatri
2019-07-14 16:41:25

This answer is correctâ âââ ââ âââ thank you so many answers are posted sir and mamdam

Prince
2019-06-15 14:57:25

Answer na aabit hau yrrr 10 ke power me garbara jaite huk

Rahul
2019-06-02 19:13:13

.3*.3=0.09 so 0.09 se 9 ko divide krne par 100 ayega

Prashant Kumar
2019-05-17 07:58:01

6.033x10^-5 ye answer aayega.

Alokananda Bhowmik
2019-04-02 09:41:46

But the answer is perfect in nootan aur calculater bhi 10^-3 dikbha rahi hain.

Prabhakar Kumar Tiwari
2019-03-29 02:09:53

Wrong Answer Right Answer= 1â¢8Ã10 ka power -3

Sahil
2019-03-28 21:36:04

I m getting 5.4 into ten to the power -4

Megha
2019-02-20 20:17:57

Heee -3 kese aya 5 ata hai am confused plz reply me fast ok how it come ....

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