1. How long must a copper wire be to have a resistance of 1 ohm if it has a squa

Question

1. How long must a copper wire be to have a resistance of 1 ohm if it has a square cross section 1mm on a side?

2. what different values of resistance can you get by combining three 6 ohm resistors?

3. Two resistors ( 4 ohms and 8 ohms) are connectred in series to a 6-v battery. What is the voltage drop across each resistor?

4. A battery is connected to a 2 ohm and 4 ohm resistor connected in parallel. The current through the battery is 3 amps. FInd the equivalent resistance of the circuit, the battery's voltage and the current in the 2 ohm resistor?

5. What equal charges would be needed for two 70 kg people to have the same electric repulsion as their gravitational attraction?

6. what is the acceleration of an electron lcoated 10 exp -12m from a fixed proton?

7. What magnetic field is required to constrain electrons moving at 6 x 10^6 m/s to a circle of radius 0.5 m?

Explanation / Answer

1) L = RA/resistivity = 1*0.001*0.001/(1.68*10^(-8)) = 59.52m

2)3, 6 ohm resitors, all in series = 18,

all in parallel = 2, 2 in parallel followed by one in series = 9,

Possible resistances are 18 ohm, 9 ohm and 2 ohm

3) Current = 6/(8+4) = 0.5 A

So voltage drop across 8 ohm = 0.5*8 = 4 V

and voltage drop across 4 ohm = 2V

4) Equivalent resistance = 2*4/(2+4) = 4/3 ohm = 1.333 ohm

So voltage of battery = I*Req = 3*4/3 = 4V

Thus current across 2 ohm resitor = 4/2 = 2 A

5)GM*M/R^2 = KQ*Q/R^2

=> Q = M *SQRT(G/K)

= 70 * sqrt( 6.67384

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