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A generator gives an average electrical power of 40 W to a lamp while its coil turns 30 times each…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A generator gives an average electrical power of W to a lamp while its coil turns times each second. Suppose that no energy is lost to friction or in the wires. What average torque must the driver supply? How much work does the driver do in one turn?
Need a reminder? The key ideaShow
A coil of turns and area turning at angular speed in a field has , with the peak emf and . The mechanical power that turns it equals the electrical power, . The average power in a resistor is .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. The power is W and Hz.
Plan. The mechanical power equals the electrical power, so .
Step 1. The angular speed. .
Step 2. The torque. We want , so .
Step 3. The work in one turn. One turn takes s. So .
Answer: N m, and J in each turn.
Check. Another way: .
Watch out. The torque is not steady, because the current rises and falls. This is the average value.
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