Electromagnetism - Simple question

In summary, the student attempted to solve a homework problem but was unable to complete the equation due to a lack of understanding. He was able to find the surface area of the ammeter due to its small size and found that the magnetic flux was 350 T.
  • #1
kalo
6
0

Homework Statement


-------/\/\/\---------
I X X X 10 Ohm X X XI
I X X X X X X X X X XI
I X X X X X X X X X XAmmeter
I X X X X X X X X X XI
I--------il-----------I
...5V

Length=10cm and width =10cm
R=10 Ohms
V=5 volts
decreasing magnetic field at rate 150T/s (into the page)

What is the reading of the Ammeter?
(Correct Answer:0.35A)

Homework Equations


I=e/R
e=BvL

The Attempt at a Solution


well basically i froze.
all i get is
s=1m (0.1x0.1)
L=40 (10x4)

From there onwards i can not link them. Probably because lacking the correct formula.
Anyway, ill much appreciate some help.
Cheers
 
Last edited:
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  • #2
Part of your given information, kinda the key part, is a rate of change of a magnetic field. Remember you also have an area you can calculate, what can you find with a magnetic field and an area?

Do you perchance have an equation among your notes and book that features a rate of change?
 
  • #3
thanks, ill take a look around the notes again
 
  • #4
still stuck
 
  • #5
Magnetic flux? -Rate of change of magnetic flux = ?


http://en.wikipedia.org/wiki/Electromagnetic_induction

Stuff like that? Unless I'm badly misinterpreting what the picture is, you've got a current flowing through the ammeter just because of the battery and the resistor, but now you have a changing magnetic field through the loop. A changing magnetic field can induce a voltage, which is what will happen here
 
  • #6
thanks again!
 
  • #7
magnetic flux = B.dS
where S is the surface area (0.01m^2).
emf is directly proportional to the rate of change of magnetic flux, so
e= d(magnetic flux) / dt -> those that mean that 150T/s = e ?
(1 T= 1Wb.m^-2)
if so then 150=Bx0.01 which makes B=15000 T
But that can't be right. I am not sure where I am going wrong...
 
  • #8
by a reversed method i go:
1. I=e/R -> 0.35=e/10 -------hence e=3.5 V
since directly prop then it becomes 3.5 Wb
2. magnetic flux= B.dS ------ 3.5= B.dS where S (surface area) = 0.1x0.1 = 0.01m^2
it comes out B= 3.5/0.01 = 350 T

But how do i do it the right way around rather then back wards :) and what formula do i use to links the initial 5V? Perhaps a formula to derive B using area and voltage (dont think there's such a formula tho)?

Just a little more help please, blochwave you been great!
 

1. What is electromagnetism?

Electromagnetism is a branch of physics that studies the relationship between electricity and magnetism. It explains how electrically charged particles interact with magnetic fields and how electric currents create magnetic fields.

2. How does an electromagnet work?

An electromagnet works by running an electric current through a wire coiled around a magnetic material, such as iron. This creates a magnetic field that can be turned on and off by controlling the flow of electricity.

3. What are some real-life applications of electromagnetism?

Electromagnetism has various real-life applications, including generators and motors, which use the relationship between electricity and magnetism to convert energy into motion. Other applications include electronic devices like speakers, computers, and televisions.

4. What is the difference between an electromagnet and a permanent magnet?

The main difference between an electromagnet and a permanent magnet is that an electromagnet can be turned on and off by controlling the flow of electricity, while a permanent magnet always has a magnetic field. Additionally, the strength of an electromagnet can be adjusted by changing the amount of current flowing through it, while the strength of a permanent magnet cannot be changed.

5. How does electromagnetic induction work?

Electromagnetic induction is the process of creating an electric current in a conductor by moving the conductor through a magnetic field. This can also be achieved by changing the strength or direction of a magnetic field near a stationary conductor. This phenomenon is the basis for generators and transformers.

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