F5 PHY CURRENT ELECTRICITY

Ian Langley

2011-10-09 7:13 am

1) http://imageshack.us/photo/my-images/217/0001fth.jpg/

Find the ammeter reading and voltmeter reading in the above figure. Assume both meters to be ideal.

2) http://imageshack.us/photo/my-images/805/0002a.jpg/

In the figure , find I1, I2 and I3 when the switch is closed.

Thank you very much please......

回答 (1)

天同

2011-10-09 8:07 am

✔ 最佳答案

1. Apply Ohm's Law to the whole circuit
8 + 6 - 6 = I.(3+9+4)
hence, I = 8/16 A = 0.5 A
Therefore, the reading on the ammeter is 0.5 A

Voltage across voltmeter = p.d across 4-ohm resistor + p.d. across 3-ohm resistor - emf of 6v cell
i.e. voltmeter reading = (-4 x0.5 - 3 x 0.5 + 6) v = 2.5 v

2. Consider the whole loop, apply Ohm's Law,
12 - 9 = 7(I1) + 8(I2) -------------------------- (1)
Consoder the left loop,
12 = 7(I1) - 4(I3) ------------------------ (2)

At the junction between the 7-ohm and 8-ohm resistors,
I2 = I1 + I3 -------------------- (3)

Solve these 3 equations for the values of I1, I2 and I3, we have,
I1 = 0.931 A
I2 = -0.44 A
I3 = -1.371 A

The -ve signs of I2 and I3 indicate the currents I2 and I3 are, in fact, flowing in the reverse direction to those shown on the figure.

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