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Questions Related to physics

If a solenoid is having magnetic moment of $0.65$J $T^{-1}$ is free to turn about the vertical direction and has a uniform horizontal magnetic field of $0.25$T applied. What is the magnitude of the torque on the solenoid when its axis makes an angle of $30^o$ with the direction of applied field?

physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

  1. $0.075$N m

  2. $0.060$N m

  3. $0.081$N m

  4. $0.091$N m

Show answer
Correct Option: C
Explanation:

Given:

The magnetic moment of the solenoid is $M=0.65\ JT^{-1}$
The magnetic field applied across the solenoid is $\ B=0.25\ T$
The angle made by the axis of the solenoid is $\theta=30^o$

The torque experienced by the solenoid is given by:
$\therefore \tau =MB\sin \theta$

$ =0.65\times 0.25\times \sin 30^o$

$=0.65\times 0.25\times \dfrac{1}{2}$

$=0.08125=0.08\ Nm$

A magnet of magnetic moment $10 \hat{i} A-m^2 $ is placed along the x-axis in a magnetic field $ \overline{B} = ( 2 \hat {i} + 3 \hat{j} )  T $ . The torque acting on bar magnet is :

physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

  1. $ 20 \hat{i} + 30 \hat{k} N-m $

  2. $20 \hat{k}  N-m $

  3. $ 30 \hat{k} N-m $

  4. $ 20 \hat{i} + 30 \hat{j}  N-m $

Show answer
Correct Option: C
Explanation:

The torque acting on bar magnet is given as,

$\tau  = M \times B$

$\tau  = \left( {10\hat i} \right) \times \left( {2\hat i + 3\hat j} \right)$

$\tau  = 30\hat k\;{\rm{N}} \cdot {\rm{m}}$

Thus, the torque acting on bar magnet is $30\hat k\;{\rm{N}} \cdot {\rm{m}}$.

A charged particle enters a uniform magnetic field with velocity vector at an angle of $45 ^o$ with the magnetic field. The pitch of the helical path followed by the particle is $p.$ The radius of the helix will be

physics magnetic effects of current and magnetism the bar magnet magnetic field due to bar magnet intensity of magnetic field and torque on a bar magnet

  1. $\dfrac { p } { \sqrt { 2 } \pi }$

  2. $\sqrt { 2 } p$

  3. $\dfrac { p } { 2 \pi }$

  4. $\dfrac { \sqrt { 2 } p } { \pi }$

Show answer
Correct Option: C

Complete the following sentences:

Like charges ...... , while unlike charges ...... each other.

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. attract, attract

  2. repel, repel

  3. attract, repel

  4. repel, attract.

Show answer
Correct Option: D
Explanation:

There are 2 types of electrical charges - positive and negative - are said to be opposite types of charge. Consistent with our fundamental principle of charge interaction, a positively charged object will attract a negatively charged object. Oppositely charged objects will exert an attractive influence upon each other. In contrast to the attractive force between two objects with opposite chargess, two objects that are of like charge will repel each other. That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart. Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other.
Therefore, Like charges repel, while unlike charges attract each other.

If two bodies A and B (A bigger in size than B) are rubbed together, then :

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. A and B get equal and opposite charges

  2. A and B get equal and similar charges

  3. A gets more charge than B, but of opposite kind

  4. A gets less charge than B, but of same kind

Show answer
Correct Option: A
Explanation:

Answer is A.

Static electricity is created when two objects are rubbed together, causing an object to give up or gain electrons. The electric charges that are created do not depend on the size of the objects. Therefore, when two bodies are rubbed together, both the bodies transfer electrons to and fro between the bodies and they obtain equal and opposite charges. The body that gives away electrons, gains positive charge and the body that obtains electrons gains negative charge.

Two uncharged bodies on rubbing, get charged due to:

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. conduction

  2. friction

  3. induction

  4. none of these

Show answer
Correct Option: B
Explanation:

Answer is B.

When two bodies are rubbed together, there is transfer of electrons because of friction.
Hence, two uncharged bodies on rubbing, gets equal and opposite charges.

A negatively charged rod is brought close to two metal spheres which are in contact with each other and the spheres are separated in the presence of the rod. Then :

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. the sphere close to the rod acquires a negative charge and the other sphere acquires a positive charge

  2. the sphere close to the rod acquires a positive charge and the other sphere acquires a negative charge

  3. both the spheres will acquire positive charge

  4. both the spheres will acquire negative charge

Show answer
Correct Option: C
Explanation:

Since the rod which was brought closer was negatively charged the induced charge acquired by the spheres will be positive. 

An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. Gravitational

  2. Magnetic

  3. Electrostatic

  4. adhesive

Show answer
Correct Option: C
Explanation:

Electrostatic force is the phenomenon that results from slow-moving or stationary electrical charges. Specifically, electrostatic force is the physical reaction that holds together the electromagnetic field created by subatomic particles, such as electrons and protons. In order for electrostatic forces to remain cohesive, these particles need to independently maintain both positive and negative charges and react to each other accordingly. 
When a balloon is rubbed with a cloth, the electrons from the atoms of the cloth enter the atoms of the balloon and the number of electrons in the atoms of balloon becomes more than the number of protons. Because of that, there is a negative charge in the balloon, and in the cloth the number of electrons in its atoms become less than the number of protons, so it's positively charged.
Therefore, due to this electrostatic force, the balloon sticks to the wall.

Like charges attract each other:

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Answer is B.

The statement is false because only unlike poles attract each other. Like poles repel each other.

A soap bubble is given a negative charge, then its radius :

physics electric fields introduction to electrostatic force electric force charging and discharging

  1. Decrease

  2. Increase

  3. Remains unchanged

  4. Can't say

Show answer
Correct Option: B
Explanation:

Answer is B.

By symmetry, the charge will distribute evenly over the surface of the bubble. Because like charges repel, they want to move even further apart, the only which way is outward, taking the soap surface with them. Of course, the increase in restoring force of the soap film (surface tension) will at some point be equal and opposite to the electrostatic force, resulting in a new (larger) equilibrium radius.
This will happen to both positive and negatively charged bubbles because of the ionic similarity.
Hence, when the soap bubble is given a negative charge, then its radius will increase.