Tag: magnetic fields and electromagnetism

Questions Related to magnetic fields and electromagnetism

In _______ Fleming Left hand rule is not used.

physics magnetic fields and electromagnetism fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

  1. Electric fan

  2. Mixer

  3. Computer

  4. Electric generator

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Correct Option: D

Fleming's left hand rule is used to find

physics magnetic fields and electromagnetism fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

  1. Direction of magnetic field 

  2. Direction of current

  3. Direction of magnetic force acting on conductor

  4. None of these

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Correct Option: A

An electron is moving vertically downwards at any place. The direction of magnetic force acting on it due to horizontal component of earth's magnetic field will be

physics magnetic fields and electromagnetism fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

  1. towards east

  2. towards west

  3. towards north

  4. towards south

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Correct Option: B
Explanation:

According to Fleming left hand rule, if the direction of horizontal component of earth's magnetic field is from south to north and direction of velocity of electron is downwards then the direction of the force given by the thumb is towards west.

An electron and a proton travel with equal speeds and in the same direction, at $90^o$ to a uniform magnetic field. They experience forces which are initially

physics magnetic fields and electromagnetism fleming's left hand rule magnetic force magnetic force on a moving charge and current carrying wire

  1. in opposite direction and differ by a factor of about 1840

  2. in the same direction and differ by a factor of about 1840

  3. equal in magnitude but in opposite directions

  4. identical

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Correct Option: C
Explanation:
As both of the particle having same speed and in the same field at same angle, they will be experiencing same force but in opposite direction as they are opposite in charge. 

A square loop of side 12 cm and resistance 0.60$\Omega$ is placed vertically in the east-west plane. A uniform magnetic field of 0.1 T is setup across the plane in north-east direction. The magnetic field is decreased to zero in 0.6 s at a steady rate. The magnitude of current during this time interval is

physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

  1. $1.42 \times 10^{-3} A$

  2. $2.67 \times 10^{-3} A$

  3. $3.41\times 10^{-3} A$

  4. $4.21 \times 10^{-3} A$

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Correct Option: B
Explanation:

Here, Area $A=l^2=(12cm)^2=1.4\times 10^{-2} m^2$
$R=0.60\omega, B _1=0.10 T,\theta=45^0$
$B _2=0,dt=0.6$ s
Initial flux,
$\phi _1=B _1Acos\theta$
      $=0.10\times1.4\times10^{-2}\times cos 45^0$
      $=9.8\times 10^{-4}$

final flux, $\phi _2$=0
Induced emf,$E=\dfrac{| d\phi |}{dt}=\dfrac{|\phi _2-\phi _1|}{dt}$
                      $E=\dfrac{|9.8\times 10^{-4}|}{0.6}s\\,\,\,\,\,=1.6\times10^{-3}V$
Current, $I=\dfrac{E}{R}=\dfrac{1.6\times\times 10^{-3}}{0.6}=2.67 \times 10^{-3}$

When the normal to a coil points in the direction of magnetic field (B), then flux is 

physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

  1. a scalar quantity

  2. a vector quantity

  3. neither scalar nor vector

  4. uncertain

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Correct Option: A
Explanation:

Dot product of field and area vectors is flux . $\Phi=B.dS$, and we know dot product of two vectors is a scalar quantity.
Therefore, flux is scalar.

Current $i _0$ is being carried by an infinite wire passing through origin along the direction $\hat{i} + \hat{j} + \hat{k}$. Find magnetic field due to the wire at point $(1 m, 0, 0)$.

physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

  1. $\dfrac{(\mu _0 i)}{(2 \pi)} T$

  2. $\dfrac{(\mu _0 i)}{(\sqrt{2} \pi)} T$

  3. $\dfrac{(\mu _0 i)}{(4 \pi)} T$

  4. $\dfrac{(\sqrt{3} \mu _0 i)}{(2 \sqrt{2} \pi)} T$

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Correct Option: D

A charge q is placed at the centre of a cylinder of radius R and length 2R. Then electric flux through the curved surface of the cylinder is 

physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

  1. $\cfrac { q }{ 2 { \epsilon } _{ 0 } } $

  2. $\cfrac { q }{ 4 { \epsilon } _{ 0 } } $

  3. $\cfrac { q }{ \sqrt { 2 } { \epsilon } _{ 0 } } $

  4. $\cfrac { q }{ 2\sqrt { 2 } { \epsilon } _{ 0 } } $

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Correct Option: C

A Point source generates 10 J of light energy in 2 s. The luminous flux of source is: 

physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

  1. 5 lumen

  2. 10 lumen

  3. 50 lumen

  4. none of these

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Correct Option: A
Explanation:

The luminous flux of source is the rate at which light energy flows from the source:

luminous flux =10 J/ 2 s= 5 lumen.
so the correct option is A.

A cyclotron in which protons are accelerated has a flux density 1.57T. The variation of frequency of electric field is (in Hz) 

physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

  1. $4.8 \times 10 ^ { 8 }$

  2. $8.4 \times 10 ^ { 8 }$

  3. $2.5 \times 10 ^ { 7 }$

  4. $4.8 \times 10 ^ { 6 }$

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Correct Option: C