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Problems involving Ohm's law

Multiple Choice

1. The resistance of a superconducting material drops, essentially to zero, rather suddenly when: (a) the sample is heated above Tc (b) the sample is exposed to a magnetic field (c) the sample is cooled below Tc (d) the sample experiences a current Ic (e) none of these. Explain your choice.

2. Imagine a length of ordinary insulated hookup wire. The wire's resistance is not dependent on: (a) the conductor's length (b) the conductors radius (c) the material making up the insulator (d) the material making up the conductor (e) none of these. Explain your choice.


1. A particle accelerator contains two beams flowing side-by-side in opposite directions; the beams will ultimately be made to collide. One is a stream of protons (each with a charge of +1.60 x 10^-19 C), the other stream of antiprotons (each with a charge of
-1.60 x 10^-19 C). Given that either beam can deliver 1.0 x 10^14 particles per second to the colliding region, what is the net current in the machine as the two streams race past each other?

2. If the current in a 10-Ohm resistor is 500mA, what is the voltage across its terminals?

3. According to the American Wire Gauge system, No. 0000 wire, which is the heaviest, has a diameter of 11.7 mm. What would be the resistance of 100 m of copper AWG No. 0000 at 20 deg C?

4. Imagine that your are going to connect a remote speaker to your stereo system. The speaker has a resistance of 4.0 Ohm, and so you want to use hookup wire whose total resistance is small by comparison, say, 0.25 Ohm. If the speaker is to be 15 m away, what diameter copper wire should be used? [Hint: you'll need two leads.]

5. What is the maximum current that should be passed through a 100-Ohm, 10-W resistor?

6. A light bulb operating a 110 V draws 1.82 A. Determine its resistance and the amount of power it draws.

7. A credit card size calculator uses two tiny 1.5-V cells in series that provide a normal operating power of 0.000 18 W. Determine the current passing through each cell when the device is in use.

Solution Preview

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(c) The sample is cooled below Tc
The main feature of superconductivity is zero electrical resistance. In the case of metals such as copper, when temperature is lowered, resistance will gradually become lower, but it will never become a zero. However, in the case of ...

Solution Summary

Example problems and solutions involving Ohm's law an DC circuits