# Solving for the unknown variable in Motional EMF problem | Physics Homework

• flyingpig
In summary, the conversation involves a student asking for clarification on a physics problem involving Lenz' Law and the calculation of speed. The student provides their attempt at a solution and realizes their initial assumption was incorrect, but then corrects it using Lenz' Law. The student then confirms their solution with a final calculation and asks for confirmation. The final answer is 1m/s.
flyingpig

## Homework Statement

http://img854.imageshack.us/img854/3980/33288207.th.png

## The Attempt at a Solution

http://img813.imageshack.us/img813/1065/60582408.th.png

$$\varepsilon = IR$$

$$\varepsilon = -\frac{d \Phi}{dt}$$

$$\Phi = BA$$

$$-\frac{d \Phi}{dt} = -Bl\frac{dx}{dt} = -Blv$$

So

$$\frac{-Blv}{R} = I$$

$$\frac{-IR}{Bl} = v$$

Now I plug in and solve, is that right or did I underestimated this question completely?

Last edited by a moderator:
Actually I just realize I assumed the current is running counter clockwise..

Actually never mind, by Lenz' Law the direction is counter clockwise for the current

Oh wait it says speed, so

$$\left | \frac{-lR}{Bl} \right | = |\vec{v}|$$

I'll just trust myself...*crickets*

Looks OK.

1m/s...

## 1. What is motional EMF and why is it important?

Motional EMF, or electromagnetic force, is the induced electric potential that is created when a conductor moves through a magnetic field. It is important because it helps explain the generation of electricity in devices such as generators and motors, and is also a fundamental concept in understanding the behavior of charged particles in magnetic fields.

## 2. How is the unknown variable in a motional EMF problem typically represented?

The unknown variable in a motional EMF problem is typically represented as "emf" or "E". This represents the induced electric potential that is generated by the motion of the conductor through the magnetic field.

## 3. What are the key equations used to solve for the unknown variable in a motional EMF problem?

The key equations used to solve for the unknown variable in a motional EMF problem are Faraday's Law, which states that the induced EMF is equal to the rate of change of magnetic flux through the conductor, and the Lorentz force law, which describes the force on a charged particle moving through a magnetic field. These equations can be combined to solve for the unknown variable in various scenarios.

## 4. What are some common examples of motional EMF in everyday life?

Some common examples of motional EMF in everyday life include the generation of electricity in power plants, the functioning of electric motors and generators, and the operation of devices such as loudspeakers, headphones, and microphones. It is also a key concept in the functioning of MRI machines in the medical field.

## 5. What are some tips for solving for the unknown variable in a motional EMF problem?

Some tips for solving for the unknown variable in a motional EMF problem include carefully defining the given variables, using the correct equations for the given scenario, and keeping track of units and signs. It can also be helpful to break down the problem into smaller steps and draw diagrams to visualize the situation. Practice and familiarity with the concept can also improve problem-solving skills in this area.

Replies
5
Views
2K
Replies
3
Views
3K
Replies
9
Views
6K
Replies
2
Views
1K
Replies
5
Views
4K
Replies
4
Views
8K
Replies
4
Views
1K
Replies
3
Views
6K
Replies
2
Views
3K
Replies
1
Views
3K