Question

electric motors convert electrical energy to mechanical energy. when a current - carrying coil is placed between the magnetic poles, a force acts on it that causes it to rotate. the image below shows a simple electric motor. what can be done to make the coil rotate faster? a. decrease the size of the magnets b. add one more battery c. use a plastic wire loop d. change the polarity of the magnets

Explanation:

Step1: Analyze each option

• Option A: Decreasing the size of the magnets would weaken the magnetic field. A weaker magnetic field would result in a smaller force acting on the current - carrying coil (using the formula \(F = BIL\sin\theta\), where \(B\) is the magnetic field strength, \(I\) is the current, \(L\) is the length of the conductor in the magnetic field, and \(\theta\) is the angle between the current and the magnetic field). So, the coil would rotate slower.
• Option B: Adding one more battery would increase the voltage in the circuit. According to Ohm's law \(I=\frac{V}{R}\) (assuming the resistance \(R\) of the circuit is constant), increasing the voltage \(V\) would increase the current \(I\). Using the formula \(F = BIL\sin\theta\), an increase in current \(I\) would increase the force \(F\) acting on the coil. A larger force would make the coil rotate faster.
• Option C: Using a plastic wire loop. Plastic is an insulator. If we use a plastic wire loop, no current would flow through the loop (since current needs a conductor to flow). Without current (\(I = 0\)), the force \(F=BIL\sin\theta = 0\) (from the formula \(F = BIL\sin\theta\)). So, the coil would not rotate at all.
• Option D: Changing the polarity of the magnets would change the direction of the force acting on the coil (using the right - hand rule for the force on a current - carrying conductor in a magnetic field). But it would not increase the magnitude of the force. So, it would change the direction of rotation, not the speed.

Answer:

B. add one more battery