# Homework Help: True or False

1. Nov 23, 2006

### cyprusx

The magnitude of the current depends on the rate at which the magnet is moving in and out of the solenoid.

True or false

2. Nov 23, 2006

### HallsofIvy

Have you considered flipping a coin?

Now you know you are expected to make some effort yourself. In this case, I assume you are talking about a generator consisting of a magnet moving inside a coil- You should have said that. What does your text book say about generators? What formulas do you know for current?

3. Nov 23, 2006

### semc

since voltage induced is proportional to the rate of change of B-field,i think magnitude is also dependent on it?

4. Nov 23, 2006

### cyprusx

i really have no clue, im a noob

5. Nov 23, 2006

### Hootenanny

Staff Emeritus
Consider Faraday's Law together with Ohm's law.

6. Nov 23, 2006

### cyprusx

man, i have too hand this in tomorrow and im at risk of failing can you cut a guy a break

7. Nov 23, 2006

### Hootenanny

Staff Emeritus
I will help you, but I am not going to give you the answer. However, if you do put some effort in, you will have the answer within minutes. Now, what is Faraday's law?

8. Nov 23, 2006

### cyprusx

Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil.

9. Nov 23, 2006

### Hootenanny

Staff Emeritus
Correct, this can be represented mathematically;

$$V=\frac{\Delta\Phi}{\Delta t}=\frac{\Delta (BA)}{\Delta t}$$

Next, what is ohm's law?

10. Nov 23, 2006

### cyprusx

Ohm's law states that, in an electrical circuit, the current passing through a conductor is directly proportional to the potential difference applied across them provided all physical conditions are kept constant.

11. Nov 23, 2006

### Hootenanny

Staff Emeritus
And mathematically;

$$I = \frac{V}{R}$$

So, can you now combine the two equations?

As an aside, I do hope that you are taking the time to understand these laws and are simply not copying and pasting them directly from the internet.

12. Nov 23, 2006

### cyprusx

how do you comine them

13. Nov 23, 2006

### Hootenanny

Staff Emeritus
Substitute Faraday's law for the V in ohm's law.

14. Nov 23, 2006

### cyprusx

cant you help a guy out

Hootenanny im studying for a test right now thats in an hour i really dont have time.

15. Nov 23, 2006

### Hootenanny

Staff Emeritus
I will do the substitution for you, however, you must draw your own conclusions. So now we can say that;

$$I = \frac{\frac{\Delta (BA)}{\Delta t}}{R} = \frac{\Delta (BA)}{R\cdot\Delta t}$$

Now, if you change that rate at which you move the magnet through the coil, do any terms change in the above equation?

16. Nov 23, 2006

### cyprusx

yes they do

17. Nov 23, 2006

### Hootenanny

Staff Emeritus
So does the current change?

18. Nov 23, 2006

### cyprusx

yes

so my initial question is False

19. Nov 23, 2006

### cyprusx

or.........

20. Nov 23, 2006

### Hootenanny

Staff Emeritus
If the current does change when you change the rate at which the magnet moves then the above statement is ____