Tag: magnetic effect of electric current

Questions Related to magnetic effect of electric current

Electromagnet can be formed due to which of the following?

physics magnetic effect of electric current oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

  1. Heating effect of current

  2. Magnetic effect of current

  3. Chemical effect of current

  4. None of the above

Show answer
Correct Option: B
Explanation:

Electromagnets are formed by passing an electric current through a wire coiled around the substance with iron core. The electric current generates a magnetic field around the  substance and thus magnetize it which convert it into a magnet. Thus electromagnet can be formed due to the magnetic effect of current.

If we change in the direction of the current passing through the wire near to the magnetic needle:

physics magnetic effect of electric current oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

  1. position of the pole of the needle will change

  2. position of the pole of the needle will remain same

  3. change in position of the pole depends on the current intensity

  4. none of the above is correct

Show answer
Correct Option: A
Explanation:

When the direction of the current flowing through the wire is reversed, direction of the magnetic field, so produced, also changes its direction which results in changing the position of pole of needle kept near the wire.

A magnetic needle vibrates in a vertical plane parallel to the magnetic meridian about horizontal axis passing through its centre. The frequency is $\pi$. If the plane of oscillation turned about a vertical axis by ${90}^{o}$, the frequency of oscillation in vertical plane will be:

physics magnetic effect of electric current oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

  1. $\pi$

  2. zero

  3. less than $\pi$

  4. more than $\pi$

Show answer
Correct Option: C
Explanation:

Frequency $\pi=\dfrac{1}{2\pi}\sqrt{\dfrac{BM}I}$

On turning through angle $90°$, effective field is $V$ and $B>V$
$\implies $ new frequqncy $<\pi$ (less than $\pi)$

What did Oersted conclude from the experiment ?

physics magnetic effect of electric current oersted experiment oersted's experiment magnetic field due to a straight current carrying conductor

  1. The current carrying wire must be acting as a magnet for the compass needle to deflect.

  2. The current carrying wire gets heated up and causes the compass needle to deflect.

  3. The current carrying wire sets up air currents that makes the compass needle to deflect.

  4. None of the above

Show answer
Correct Option: A
Explanation:

The deflection of the compass needle, whenever there is current in the wire show that a current carrying wire produces a magnetic field around it, which is essentially saying the current carrying wire must be acting as a magnet.

A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is

physics magnetic effect of electric current magnetic field lines due to current magnetic field due to current carrying conductor magnetic field on the axis of a toroid

  1. 4 B

  2. B/2

  3. B

  4. 2 B

Show answer
Correct Option: C
Explanation:

$\displaystyle B = \mu _0 N _0  i;   $

$B _1 = (\mu _0) \left ( \dfrac{N _0}{2} \right ) (2 i) $

$= \mu _0 N _0 i = B$


$\Rightarrow B _1 = B$

A wire 28 m long is bent into N turns of circular coil of diameter 14 cm forming a solenoid of length 60 cm. Calculate the magnetic field inside it when a current of 5 amp passed through it.  $(\mu _0 = 12.57 \times 10^{-7} m^{-1})$

physics magnetic effect of electric current magnetic field lines due to current magnetic field due to current carrying conductor magnetic field on the axis of a toroid

  1. $6.67 \times10^{-1} T$

  2. $6.67 \times10^{-4} T$

  3. $6.67 \times10^{4} T$

  4. $2.67 \times10^{-4} T$

Show answer
Correct Option: B
Explanation:

Given $d = 14 cm=0.14 m$    

           $l = 60cm = 0.6 m$

By the question, $N \times \pi d = 28 m.$

$N \times \pi \times 0.14 = 28$

$\displaystyle \therefore N = \dfrac{28}{0.14 \times \pi} = 63.66 turns$

$\displaystyle B = \mu _o   nI  =\mu _o  \dfrac{N}{l} I = 12.57 \times 10^{-7} \times \dfrac{63.66}{0.6} \times 5$

$=6.67 \times10^{-4} T$

The electric current in a circular coil of two turns produced a magnetic induction of $0.2 T$ at its centre. The coil is unwound and is rewound into a circular coil of four turns. The magnetic induction at the centre of the coil now is, in $T$ :
(if same current flows in the coil)

physics magnetic effect of electric current magnetic field lines due to current magnetic field due to current carrying conductor magnetic field on the axis of a toroid

  1. $0.2$

  2. $0.4$

  3. $0.6$

  4. $0.8$

Show answer
Correct Option: D
Explanation:

Coil is unwound and is rewound into a circular coil of 4 turns,
$\therefore $ $2\pi R=4\times 2\pi r$ 
$r=\dfrac{R}{4}$
$\left | B \right | =\dfrac{\mu _{0}I}{\dfrac{2R}{4}}$ $=0.2\times$ $4=0.8T$

A circular coil of wire of $n$ turns has a radius $r$ and carries a current $i$. Its magnetic dipole moment is $M$. Now the coil is unwound and again rewound into a circular coil of half the initial radius and the same current is passed through it, then the dipole moment of this new coil is :

physics magnetic effect of electric current magnetic field lines due to current magnetic field due to current carrying conductor magnetic field on the axis of a toroid

  1. $\dfrac{M}{2}$

  2. $\dfrac{M}{4}$

  3. $M$

  4. $2M$

Show answer
Correct Option: A
Explanation:

The length of remains same $N _1\pi*r=N _2\pi*r/2$


$N _2=2n$

$M=NAI=nI\pi*r^2$

$M _2=N _2I*\pi*(r/2)^2=2n*I\pi*(r^2/4)$

$\dfrac{M _2}{M}=\dfrac{1}{2}$

$M _2=\dfrac{M}{2}$

A rectangular coil of wire of $500$ turns of area $10\times 5cm^{2}$ carries a current of $2 A$ in a magnetic field of induction $2\times 10^{-3}T$ . If the plane of the coil is parallel to the field. The torque on the coil is (in$ Nm$):

physics magnetic effect of electric current magnetic field lines due to current magnetic field due to current carrying conductor magnetic field on the axis of a toroid

  1. $0.1$

  2. $0.01$

  3. $0.001$

  4. $1$

Show answer
Correct Option: B
Explanation:

The torque on the rectangular coil due to presence of magnetic field is given, 

$\tau=NIAB\sin\theta$
where number of turns $N=500$,
Current in the coil $I=2A$, 
Area of the coil  $A=(10\times 5)10^{-4} m^2$,
Magnetic field $B=2\times 10^{-3}T$,
Angle between area and magnetic field vector is $\theta$ 
As area vector is always normal to plane and given the plane is parallel to field, so the angle between area and field is $90^o$.
So, $\tau=500\times 2\times (10\times 5)\times 10^{-4}\times (2\times 10^{-3})sin90=0.01 \, Nm$

A current I ampere flows along an infinitely long straight thin walled hollow metallic cylinder of radius r . The magnetic field at any point inside the cylinder at a distance x from the axis of the cylinders is :

physics magnetic effect of electric current magnetic field lines due to current magnetic field due to current carrying conductor magnetic field on the axis of a toroid

  1. $\dfrac{\mu _{0}I}{4\pi r}$

  2. $\dfrac{\mu _{0}I}{2\pi r}$

  3. $\dfrac{\mu _{0}I}{2\pi x}$

  4. zero

Show answer
Correct Option: D
Explanation:

$\oint B\cdot dl=\mu _0 I _{enclosed}$
Here,
$I _{enclosed}=0$
So,  B $=0$