Tag: magnetic fields and electromagnetism

Quizzes (4) Questions (46)

Questions Related to magnetic fields and electromagnetism

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

In _______ Fleming Left hand rule is not used.

  1. Electric fan

  2. Mixer

  3. Computer

  4. Electric generator
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Fleming's left-hand rule is used for electric motors, which convert electrical energy into mechanical energy. An electric generator uses Fleming's right-hand rule, as it converts mechanical energy into electrical energy.

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

Fleming's left hand rule is used to find

  1. Direction of magnetic field

  2. Direction of current

  3. Direction of magnetic force acting on conductor

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Fleming's left hand rule states that if the thumb, forefinger, and middle finger of the left hand are mutually perpendicular, the forefinger points in the direction of the magnetic field, the middle finger in the direction of current, and the thumb points in the direction of the magnetic force acting on the conductor.

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

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

  1. towards east

  2. towards west

  3. towards north

  4. towards south
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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. 
Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

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

  1. $1.42 \times 10^{-3} A$
  2. $2.67 \times 10^{-3} A$
  3. $3.41\times 10^{-3} A$
  4. $4.21 \times 10^{-3} A$
Reveal answer Fill a bubble to check yourself
B Correct answer
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, $I=\dfrac{E}{R}=\dfrac{1.6\times\times 10^{-3}}{0.6}=2.67 \times 10^{-3}$

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

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

  1. a scalar quantity

  2. a vector quantity

  3. neither scalar nor vector

  4. uncertain
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 $(1 m, 0, 0)$.

  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. $\dfrac{(\sqrt{3} \mu _0 i)}{(2 \sqrt{2} \pi)} T$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The magnetic field B = (mu_0 * i) / (2 * pi * r). The distance r from the wire (passing through origin along 1,1,1) to (1,0,0) is the perpendicular distance. Using the cross product formula for distance from a point to a line, r = |(r_p - r_0) x u| = |(1,0,0) x (1/sqrt(3), 1/sqrt(3), 1/sqrt(3))| = |(0, -1/sqrt(3), 1/sqrt(3))| = sqrt(2/3). B = (mu_0 * i) / (2 * pi * sqrt(2/3)) = (sqrt(3) * mu_0 * i) / (2 * sqrt(2) * pi).

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

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 

  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 } } $
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

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

  1. $4.8 \times 10 ^ { 8 }$
  2. $8.4 \times 10 ^ { 8 }$
  3. $2.5 \times 10 ^ { 7 }$
  4. $4.8 \times 10 ^ { 6 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cyclotron frequency f = qB / (2 * pi * m). For protons, q = 1.6e-19 C, m = 1.67e-27 kg, B = 1.57 T. f = (1.6e-19 * 1.57) / (2 * 3.14 * 1.67e-27) approx 2.4e7 Hz.