Torque on a Dipole

Q.

An electric dipole is placed at an angle of 30° with an electric field intensity of 2 × ${10}^5$ N/C. It experiences a torque equal of 4 Nm. The charge on the dipole, if the dipole length is 2 cm, is

1. 5 mC
2. 8 mC
3. 7 μC
4. 2 mC

Q.

When an electric dipole is placed in a uniform electric field, it experiences?

Q. An electric dipole is kept in non-uniform electric field. It experiences

1. A force and a torque
2. A torque but not a force
3. Neither a force nor a torque
4. A force but not a torque

Q.

What will happen to an electric dipole placed in a non uniform electric field

Q.

An electric dipole with dipole moment $4\times {10}^{–9}$ C m is aligned at ${30}^{\circ }$ with the direction of a uniform electric field of magnitude $5\times {10}^{4}N{C}^{–1}$. Calculate the magnitude of the torque acting on the dipole.

Q. The torque acting on a dipole of moment $\overrightarrow{P}$ in an electric field $\overrightarrow{E}$ is

1. $\overrightarrow{P}.\overrightarrow{E}$
2. $\overrightarrow{P}\times \overrightarrow{E}$
3. $Zero$
4. $\overrightarrow{E}\times \overrightarrow{P}$

Q. A point particle of mass $M$ is attached to one end of a massless rigid non-conducting rod of length $L$. Another point particle of same mass is attached to the other end of the rod. The two particles carry charges $+q$ and $-q$ repectively. This arrangement is held in a region of uniform electric field $E$ such that the rod makes a small angle $(\theta <5^{\circ })$ with the field direction. The minimum time needed for the rod to become parallel to the field after it is set free. (rod rotates about centre of mass)

1. $2\pi \sqrt{\frac{ML}{2qE}}$
2. $\pi \sqrt{\frac{ML}{2qE}}$
3. $\frac{\pi }{2}\sqrt{\frac{ML}{2qE}}$
4. $4\pi \sqrt{\frac{ML}{2qE}}$

Q.

Two equal and opposite charges of $4\times {10}^{-8}C$ when placed $2\times {10}^{-2}cm$ away, form a dipole. If this dipole is placed in an external electric field of $4\times {10}^8$ newton/coulomb, the value of maximum torque and the work done in rotating it through ${180}^o$ will be

1. $64\times {10}^{-4}Nmand64\times {10}^{-4}J$
2. $32\times {10}^{-4}Nmand32\times {10}^{-4}J$
3. $32\times {10}^{-4}Nmand64\times {10}^{-4}J$
4. $64\times {10}^{-4}Nmand32\times {10}^{-4}J$

Q. A neutral pendulum oscillates in a uniform electric field as shown in figure. If a positive charge is given to the pendulum, then its time period
Assume that $mg>qE$

1. will increase.
2. will decrease.
3. will remain constant.
4. will first increase then decrease.

Q. A sample of $\text{HCl}$ gas is placed in an electric field of $2.5\times {10}^4\text{N/C}$. The dipole moment of each $\text{HCl}$ molecule is $3.4\times {10}^{-30}\text{C-m}$. Find the maximum torque that can act on a molecule.

1. $6.5\times {10}^{-26}\text{N-m}$
2. $7.5\times {10}^{-26}\text{N-m}$
3. $8.5\times {10}^{-26}\text{N-m}$
4. $9.5\times {10}^{-26}\text{N-m}$

Q. point charge of 0.009 uC is placed at origin. Theintensity of electric field due to this charge at apoint (\sqrt{}2, \sqrt[{}]{}7, 0) is(1) (3/\sqrt{}2i+3 7) NC-(2) (2./3 i +3.7j) NC-1(3) (3/21+7 3\rbrack) NC-(4) (21+7/3) NC-

Q. A particle performing simple harmonic motion undergoes displacement of $\frac{A}{2}$ (where $A$ is the amplitude of simple harmonic motion) during first second. At $t=0$, the particle may be at the extreme position or mean position. The period of the simple harmonic motion can be

1. $6\text{s}$
2. $2.4\text{s}$
3. $12\text{s}$
4. $1.2\text{s}$

Q. What is tension in ring due to its own charge ?

Q. An electric dipole of dipole moment p is placed in the position of stable equilibrium in uniform electric field of intensity E. This is rotated through an angle theta from the initial position. The potential energy of the electric dipole in the final position is (1) -pE cos theta (2) pE (1-cos theta) (3) pE cos theta (4) pE sin theta

Q.

A uniform magnetic field of 3000 G is established along the positive z-direction. A rectangular loop of sides 10 cm and 5 cm carries a current of 12 A. What is the torque on the loop in the different cases shown in Fig. 4.28? What is the force on each case? Which case corresponds to stable equilibrium?

Q. A rigid wire loop of square shape having side of length $L$ and resistance $R$ is moving along the $x$-axis with a constant velocity $v_0$ in the plane of the paper. At $t=0$, the right edge of the loop enters a region of length $3L$ where there is a uniform magnetic field $B_0$ into the plane of the paper, as shown in the figure. For sufficient large $v_0$, the loop eventually crosses the region. Let $x$ be the location of the right edge of the loop. Let $v\left(x\right),I\left(x\right)$ and $F\left(x\right)$ represent the velocity of the loop, current in the loop, and force on the loop, respectively, as a function of $x$. Counter-clockwise current is taken as positive.
Which of the following schematic plot(s) is (are) correct? (Ignore gravity)

1. 
2. 
3. 
4. 

Q. A block of mass $m$ is constrained to move inside a ring of radius $R$ which is fixed on a horizontal smooth table. At time $t=0$, block is moving along the inside of the ring (i.e., in the tangential direction) with velocity $v_0$. The coefficient of friction between the block and the ring is $\mu$. Then the speed of the block at time $t$ is

1. $\frac{v_0}{R+\mu v_{0}t}$
2. $\frac{v_0}{(1+\frac{\mu v_{0}t}{R})}$
3. $\frac{v_0}{1-\frac{\mu v_{0}t}{R}}$
4. $\frac{v_{0}R}{1+\mu v_{0}t}$

Q. A plastic rod has a uniformly distributed charge q the rod has been bent in a 2 theta circular arc of radius R.What is the electric field and potential due to rod at point p

Q. An electric dipole consisting of two opposite charges of $2\times {10}^{-6}C$ separated by a distance of 3cm is placed in an electric field of $2\times {10}^{5}N/C$. The maximum torque on the dipole will be

1. $12\times {10}^{–1}Nm$
2. $12\times {10}^{–3}Nm$
3. $24\times {10}^{–1}Nm$
4. $24\times {10}^{–3}Nm$

Q. In which orientation, a dipole placed in a uniform electric field is in (i) stable equilibrium (ii) unstable equilibrium?

Q. An electric dipole is placed in an electric field generated by a point charge.
(a) The net electric force on the dipole must be zero.
(b) The net electric force on the dipole may be zero.
(c) The torque on the dipole due to the field must be zero.
(d) The torque on the dipole due to the field may be zero.

Q. when dipole is placed in a uniform electric field net force on it is 0 but torque is not 0. but according to formula τ=rFsinθ, as F is 0 so τ should be 0?

Q.

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?

Q. The torque acting on a dipole of moment $\overrightarrow{p}$ in an electric field $\overrightarrow{E}$ is .

1. $\overrightarrow{p}.\overrightarrow{E}$
2. $\overrightarrow{p}X\overrightarrow{E}$
3. $Zero$
4. $\overrightarrow{E}X\overrightarrow{p}$

Q. A closely wound solenoid of 800 turns and area of cross section2.5 × 10–4 m2 carries a current of 3.0 A. Explain the sense in which the solenoid acts like a bar magnet. What is its associated magnetic moment?

Q. A simple pendulum with a bob of mass $m=1\text{kg}$, charge $q=5\mu \text{C}$ and string length $l=1\text{m}$ is given a horizontal velocity $u$ in a uniform electric field $E=2\times {10}^6\text{V/m}$ at its bottom most point $\text{A}$ as shown in figure. It is given that the speed $u$ is such that the string slacks at point $\text{C}$. Find the speed $u$.
[Take $g=10{\text{m/s}}^2$]

1. $\sqrt{37}\text{m/s}$
2. $5\text{m/s}$
3. $\sqrt{31}\text{m/s}$
4. $7\text{m/s}$

Q. When an electric dipole is placed in a non uniform electric field, what the dipole experience ?

Q. In a certain region of space, electric field is along the z-directionthroughout. The magnitude of electric field is, however, not constant but increases uniformly along the positive z-direction, at the rate of105 NC–1 per metre. What are the force and torque experienced by asystem having a total dipole moment equal to 10–7 Cm in the negativez-direction ?

Q. State the $SI$ unit of magnetic dipole moment

Q. An electric dipole placed in a non-uniform electric field experiences :

1. both, a torque and a net force
2. only a force but no torque
3. only a torque but no net force
4. no torque and no net force