Electric Charges and Fields Physics - Electric Charges and Fields

If the net electric flux through a closed surface is zero, then we can infer:

A metallic solid sphere is placed in a uniform electric field. The electric field lines follow the path(s) shown in figure as

Two point positive charge of 1C are located at a distance 1 m from each other in the air. The value of the electric force of repulsion acting between the charges will be-

Mark out the correct options.

When the object has no electric charge then the object is said to be:

For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): Charge is quantized.
Reason (R): Charge which is less than I C is not possible.

For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): The electric tines of forces diverges from a positive charge and converge at a negative charge.
Reason (A): A charged particle free to move in an electric field always move along an electric line of force.

For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): Charging is due to transfer of electrons.
Reason (R): Mass of a body decreases slightly when it is negatively charged.

For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): If there exists coulomb attraction between two bodies, both of them may not be charged.
Reason (R): ln coulomb attraction two bodies are oppositely charged.

For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false and R is also false.

Assertion (A): If a conducting medium is placed between two charges, then electric force between them becomes zero.
Reason (R): Reduction in a force due to introduced material is inversely proportional to its dielectric constant.

What is the net flux of the uniform electric field of Exercise 1.15 through a cube of side 20 cm oriented so that its faces are parallel to the coordinate planes?

Why do the electric field lines never cross each other?

Define dielectric constant of a medium. What is its S.I. unit?

Why do the electrostatic field lines not form closed loops?

Two equal balls having equal positive charge ‘q’ coulombs are suspended by two insulating strings of equal length. What would be the effect on the force when a plastic sheet is inserted between the two?

When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

An infinite line charge produces a field of 9 × 10⁴ N/C at a distance of 2 cm. Calculate the linear charge density.

A uniformly charged conducting sphere of 2.4 m diameter has a surface charge density of 80.0 μC/m².

1. Find the charge on the sphere.
2. What is the total electric flux leaving the surface of the sphere?

An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 × 10⁴ NC^-1 in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm^-3. Estimate the radius of the drop. (g = 9.81 m s^-2; e = 1.60 × 10^-19 C).

A polythene piece rubbed with wool is found to have a negative charge of 3 × 10^-7 C.

1. Estimate the number of electrons transferred (from which to which?)
2. Is there a transfer of mass from wool to polythene?

Consider a uniform electric field E = 3 × 10³ î N/C.

1. What is the flux of this field through a square of 10 cm on a side whose plane is parallel to the yz plane?
2. What is the flux through the same square if the normal to its plane makes a 60° angle with the x-axis?

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?

Figure 1.33 shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

The electric current flowing in a wire in the direction from B to A is decreasing. Find out the direction of the induced current in the metallic loop kept above the wire as shown.

Electric field strength is proportional to the density of lines of force i.e., electric field strength at a point is proportional to the number of lines of force cutting a unit area element placed normal to the field at that point. As illustrated in the given figure, the electric field at P is stronger that at Q.

1. Electric lines of force about a positive point charge are:

1. Radially outwards.
2. Circular clockwise.
3. Radially inwards.
4. Parallel straight lines.

2. Which of the following is false for electric lines of force?

1. They always start from positive charges and terminate on negative charges.
2. They are always perpendicular to the surface of a charged conductor.
3. They always form closed loops.
4. They are parallel and equally spaced in a region of uniform electric field.

3. Which one of the following pattern of electric line of force in not possible in filed due to stationary charges?

1.  

2.  

3.  

4.  

4. Electric lines of force are curved:

1. In the field of a single positive or negative charge.
2. In the field of two equal and opposite charges.
3. In the field of two like charges.
4. Both (b) and (c).

5. The figure below shows the electric field lines due to two positive charges. The magnitudes E_A, E_B and E_C of the electric fields at points A, Band C respectively are related as:

1. E_A > E_B > E_C
2. E_B > E_A > E_C
3. E_A = E_B > E_C
4. E_A > E_B = E_C

Check that the ratio ke²/G m_em_p is dimensionless. Look up a Table of Physical Constants and determine the value of this ratio. What does the ratio signify?

It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge + (2/3) e, and the ‘down’ quark (denoted by d) of charge (–1/3) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

In a certain region of space, electric field is along the z-direction throughout. The magnitude of electric field is, however, not constant but increases uniformly along the positive z-direction, at the rate of 10⁵ NC^-1 per metre. What are the force and torque experienced by a system having a total dipole moment equal to 10^-7 Cm in the negative z-direction?

A particle of mass m and charge (–q) enters the region between the two charged plates initially moving along x-axis with speed vx (like particle 1 in Fig. 1.33). The length of plate is L and an uniform electric field E is maintained between the plates. Show that the vertical deflection of the particle at the far edge of the plate is qEL² /(2m v² x).
Compare this motion with motion of a projectile in gravitational field discussed in Section 4.10 of Class XI Textbook of Physics.