Eddy Currents

Q. What is the magnitude of electric field intensity due to a short dipole of moment of magnitude $2\times {10}^{-8}\text{C -m}$ at a point $1\text{m}$ from the centre of the dipole, when the line joining the point to the centre of the dipole makes an angle of ${60}^{\circ }$ with the dipole axis?

1. $170\text{N/C}$
2. $193\text{N/C}$
3. $200\text{N/C}$
4. $238\text{N/C}$

Q.

What are Eddy Currents? Explain how they are produced and how they can be minimised. Give two uses of eddy current.

Q. Explain how Lenz law follows law of conservation of energy

Q. An electric dipole is placed perpendicular to an infinite line of charge at some distance from it as shown in the figure. Then the dipole

1. is attracted towards the line charge
2. is repelled away from the line charge
3. does not experience a force
4. is experienced force as well as torque

Q. Eddy currents are produced when

1. a metal is kept in a varying magnetic field
2. a metal is kept in a steady magnetic field
3. a circular coil is placed in a magnetic field
4. current is passed through a circular coil

Q. Find the magnitude of electric field due to a dipole at a point $\text{P}$ along the line joining point $\text{P}$ and centre of dipole as shown in figure.

1. $2.0\times {10}^{-3}\text{N/C}$
2. $3.5\times {10}^{-3}\text{N/C}$
3. $3.0\times {10}^{-3}\text{N/C}$
4. $2.5\times {10}^{-3}\text{N/C}$

Q.

A point source of electromagnetic radiation has an average power output of $1500W$. The maximum value of the electric field at a distance of $3m$ from this source in $V{m}^{-1}$ is

1. $500$

2. $100$

3. $\frac{500}{3}$

4. $\frac{250}{3}$

5. $10\sqrt{5}$

Q.

What is polarization density?

Q. What is the angle between plane of eddy currents and the plane of magnetic field?

1. $0^{\circ }$
2. ${60}^{\circ }$
3. ${90}^{\circ }$
4. ${180}^{\circ }$

Q.

An electric current produces a heating effect but not a magnetic effect.

1. True
2. False

Q. A very small circular loop of area $5\times {10}^{-4}{\text{m}}^2$ of resistance $2\Omega$ and negligible inductance is initially coplanar and concentric with a much larger fixed circular loop of radius $0.1\text{m}$. A constant current of $1\text{A}$ is passed in the bigger loop and the smaller loop is rotated with angular velocity $1\text{rad/s}$ about a diameter. Calculate the maximum flux linked with the smaller loop.

1. $2\pi \times {10}^{-9}\text{Wb}$
2. $4\pi \times {10}^{-9}\text{Wb}$
3. $\pi \times {10}^{-9}\text{Wb}$
4. $\frac{\pi }{2}\times {10}^{-9}\text{Wb}$

Q. The current flowing in two coaxial coils is in the same direction. On increasing the distance between the two, the electric current will-

1. Increase
2. Decrease
3. Remain unchanged
4. Initially increases and decreases.

Q. A parallel plate condenser has initially air medium between the plates.if a slab of dielectric constant 5 having thickness half the distance of separation between the plates is introduced the percentage increase in its capacity is.

Q.

A coil of area 100 cm^2 having 500 turns carries a current of 1 m A. It is suspended in a uniform magnetic field of induction 10^-3wb/m^2. Its plane making an angle of 60° with the lines of induction. the torque acting on the coil is

Q.

Prove that electromagnetic induction is conservation of energy in nature?

Q. A coaxial cable consists of a thin inner current carrying wire fixed along the axis of a hollow current carrying tube. Let $B_{1}and{B}_2$ be the magnetic fields in the region between the conductors and outside the tube respectively, then:

1. $B_1\ne 0,B_2\ne 0$, for the conductors carrying equal currents in opposite directions.
2. $B_1\ne 0,B_2=0$, for the conductors carrying equal currents in opposite directions.
3. $B_1\ne 0,B_2\ne 0$, for the conductors carrying equal currents in same directions.
4. $B_1\ne 0,B_2=0$, for the conductors carrying equal currents in same directions.

Q. A heater coil boils certain amount of water in 10minute.Another heater coil boils the same amount of water in 15minute.If both heaters are used in series to boil the same amount of water, then time taken will be

Q. A bar magnet is released into a copper tube. Mass of the magnet is $m$. After some time it gains a constant speed of $v_0$, then heat developed per second in conducting cylinder will be,

1. $\frac{3}{2}mg{v}_0$
2. $\frac{mg{v}_0}{2}$
3. $mg{v}_0$
4. zero

Q.

A light metal disc on the top of an electromagnet is thrown up as the current is switched on. Why ? Give reason.

Q.

Eddy currents are produced due to changes in?

Q.

Assertion: If a current is flowing through a machine of iron, eddy currents are produced.

Reason: The change in magnetic flux through an area causes eddy current

1. Both A and R are true and R is the correct explanation

2. A is true but R is false

3. Both A and R are false

4. Both A and R are true but R is not the correct explanation

Q. Induction cooker works on the principle of:

1. 40^o
2. 0^o
3. 90^o
4. 180^o

Q. Two circular loops are placed with their centers separated by a fixed distance. Their orientation, such that they have the zero mutual inductance, is -

1. The two loops should be placed co-axially with planes in parallel.
2. The two loops should be placed such that their axes are perpendicular.
3. Either $\left(A\right)$ or $\left(B\right)$
4. None of these

Q. A rod of length $3\text{m}$ is kept parallel to a long wire carrying constant current $0.5\text{A}.$ It is moving away from the wire with a velocity of $10\text{m/s}.$ Find the induced emf in the rod when its distance from the long wire is $0.15\text{m}.$

1. $3\times {10}^{-3}\text{V}$
2. $2\times {10}^{-6}\text{V}$
3. $5\times {10}^{-4}\text{V}$
4. $2\times {10}^{-5}\text{V}$

Q. A magnet drops down a long vertical copper tube. its velocity as it falls down the tube
a)increases
b)remains constant
c)decreases
d)first increase and then decreases

Q.

Why do the eddy currents have a negative effect, as they produce?

Q.

A current I flows along infinitely long straight thin counductor , then magnetic field induction at any point on the counductor is

1. zero

2. Infinity

3. 2I/r

4. 

Q. A straight conductor of length 4 m moves at a speed of 5 ms−1 perpendicular to its length. When the conductor makes an angle of 30º with the direction of magnetic field of induction of 0.2 T, then induced emf is (Conductor, velocity and magnetic field, all lie in XY plane)

Q. Induction cooker works on the principle of:

1. Magnetic Force
2. Electromagnetic Induction
3. Damped Oscillations
4. Eddy Currents

Q. What are eddy currents ?
How are eddy currents reduced in metallic cores ?
State two uses of eddy currents.