Basic Elecricity

1. Oct 28, 2006

Energize

Can someone please check my answers here, there are loads of formulaes been give that I haven't used so I'm not sure if they are right or not, thanks.

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2. Oct 29, 2006

Staff: Mentor

The first problem (resistors in series) is done correctly, but the second (resistors in parallel) is not. Recalculate the total resistance in that second circuit. Hint: When resistors are in parallel, the total resistance will be less than that of any single resistor.

3. Oct 29, 2006

andrevdh

The total resistance of resistors in parallel can be calculated with

$$\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2}$$

this can be changed to

$$R_p=\frac{R_1R_2}{R_1 + R_2}$$

4. Oct 29, 2006

Energize

When I do that I get 6x2 = 12ohm 12ohm/8 ohms = 1.5 ohms, is that right?

5. Oct 29, 2006

andrevdh

Yes. That seems to be it.

6. Oct 29, 2006

Energize

Am I right in thinking that if you have a 12v battery and short it the current would be very high?

Last edited: Oct 29, 2006
7. Oct 29, 2006

andrevdh

Not neccessarily. The amp-hours rating is a complicated affair. It is the amount of current it can supply (chosen for "normal" [designed] operating conditions) for a certain set period (I think it is normally for 20 hours, but I might be wrong) before the battery is completely drained and dies out. So you might get more out of it for a shorter period but only to a certain limit (everyone has his limitations!).

8. Oct 29, 2006

Energize

Ok I think I'm not sure If I've got this right. I worked out I1 and I2 using fractions.

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9. Oct 30, 2006

Energize

Anyone?.........

10. Oct 30, 2006

Staff: Mentor

11. Oct 30, 2006

andrevdh

The current through the 2 ohm resistor is the current through all of the circuit since

$$I = I_1 + I_2$$

So $$I$$ will be be determined by the total resistance of the circuit and the voltage of the power supply.

12. Oct 31, 2006

Energize

Ok we went through that question today and I got A-F right but G was 0.9A.

13. Oct 31, 2006

CPL.Luke

12/5 does not equal 1.2, maybe you sent us the wrong version of the problem, or the teacher did it wrong

14. Oct 31, 2006

Energize

Ah sorry I put 12v instead of 6, doh.