In view of the coronavirus pandemic, we are making LIVE CLASSES and VIDEO CLASSES completely FREE to prevent interruption in studies
Physics > Electromagnetic Induction > Motional Electromotive Force
Electromagnetic Induction

Motional Electromotive Force

Did you know that the Electromotive force is essential for an electronic circuit to drive currents through the circuit? The electromotive force also like a charge pump. Let us learn more about them.

Suggested Videos

Play
Play
Play
Arrow
Arrow
ArrowArrow
Introduction to Electromagnetic Induction H
Eddy Current
Introduction of Magetic flux Hindi
Slider

 

Motional Electromotive Force

An emf induced by the motion of the conductor across the magnetic field is a motional electromotive force. The equation is given by E = -vLB.  This equation is true as long as the velocity, field, and length are mutually perpendicular. The minus sign associated with the Lenz’s law.

Motional Electromotive Force(Source: Exam.com)

For us to understand the motional electromotive force, let us make a particular setup. Let us take a rectangular coil, a metal rod of length L, moving with velocity V, through a magnetic field B. There is a magnetic field at some location.

Length, velocity and magnetic field should always be at a right angle with each other. The direction of the magnetic field is going inside. Assume the metal rod is frictionless that means there is no loss of energy due to friction and we apply a uniform magnetic field. The conductor rod is moved with a constant velocity and placed in the magnetic field.

Browse more Topics under Electromagnetic Induction

ΦB = Blx

But ‘x’ changes with time,

E = – \( \frac{dΦ_B}{dt} \) = – \( \frac{d }{dt} \) (Blx) = -Bl \( \frac{dx}{dt} \)

E = Blv

The induced emf Blv is motion electromotive force. So we produce emf by moving a conductor inside the uniform magnetic field. The power required to move a conductor rod in a magnetic field is,

P =  \( \frac{B² l² v²}{R} \)

Where,

  • B is the magnetic field,
  • l is the length of the conductor
  • v is the velocity of the conductor
  • R is the resistance

The magnetic flux associated with the coil is given by Φ = BA cos θ. We know that cos θ = 0, so Φ = BA. The motion of electromotive force can be further explained by Lorentz force which acts on free charge carriers. The Lorentz force on charge is:

F = qVB

You can download Electromagnetic Induction Cheat Sheet by clicking on the download button below
Motional Electromotive Force

 

Solved Questions For You

Q1. A coil having n turns and area A is initially placed with its plane normal to the magnetic field B. It is then rotated through 180º in 0.2 sec. The emf induced at the ends of the coils is

  1. 0.1 nAB
  2.  nAB
  3. 5 nAB
  4. 10 nAB

Answer: D. Total change in flux = ΔΦ = 2 nAB
Total time of change = Δt = 0.2s
Emf induced = \( \frac{ΔΦ}{Δt} \) = 10nAB

Q2.  A straight line conductor of length 0. 4m is moved with a speed of 7ms-1 perpendicular to a magnetic field of an intensity of 0.9wbm-2  The induced emf across the conductor is:

  1. 25.2 V
  2. 5.24 V
  3. 2.52 V
  4. 1.26 V

Answer: C. The induced emf across the conductor E= Blv
= 0.98 × 0.4 × 7 = 2.52V

Q.3 Two conducting rings of radii r and 2r move in opposite directions with velocities 2v and v respectively on a conducting surface S. There is a uniform magnetic field of magnitude B perpendicular to the plane of the rings. The potential difference between the highest points of the two rings is:

  1. Zero
  2. 2rvB
  3. 4rvB
  4. 8rvB

Answer: D. Replace the emf in the rings by the cells.
E1= B2r(2V) = 4Brv
E= B(4r)v  = 4Brv
V–  V= 8Brv

Share with friends

Customize your course in 30 seconds

Which class are you in?
5th
6th
7th
8th
9th
10th
11th
12th
Get ready for all-new Live Classes!
Now learn Live with India's best teachers. Join courses with the best schedule and enjoy fun and interactive classes.
tutor
tutor
Ashhar Firdausi
IIT Roorkee
Biology
tutor
tutor
Dr. Nazma Shaik
VTU
Chemistry
tutor
tutor
Gaurav Tiwari
APJAKTU
Physics
Get Started

2
Leave a Reply

avatar
1 Comment threads
1 Thread replies
1 Followers
 
Most reacted comment
Hottest comment thread
2 Comment authors
Pandit salekarPratik salekar Recent comment authors
  Subscribe  
newest oldest most voted
Notify of
Pratik salekar
Guest
Pratik salekar

It is good but not best

Pandit salekar
Guest
Pandit salekar

Yes it is not excellent a learning website

Kaka
Guest
Kaka

Then which one u prefer?

srinithi
Guest
srinithi

quora , learn cbse,meritnation

dsk
Guest
dsk

brainly also

Stuck with a

Question Mark?

Have a doubt at 3 am? Our experts are available 24x7. Connect with a tutor instantly and get your concepts cleared in less than 3 steps.
toppr Code

chance to win a

study tour
to ISRO

Download the App

Watch lectures, practise questions and take tests on the go.

Get Question Papers of Last 10 Years

Which class are you in?
No thanks.