A motor contains a coil with a total resistance of 10 ohms and is supplied by a voltage of 120v. When the motor is running at its maximum speed, the back emf is 70v.
A. Find the current in the coil at the instant the motor is turned on.
B. Find the current in the coil when the motor has reached maximum speed
A. To find the current in the coil at the instant the motor is turned on, we need to calculate the voltage across the coil. This can be done using Ohm's Law, which states that voltage (V) equals current (I) multiplied by resistance (R): V = I * R.
Given that the voltage supplied is 120V and the resistance of the coil is 10 ohms, we can rearrange the equation to solve for the current: I = V / R.
Plugging in the values, we have: I = 120V / 10 ohms = 12A.
Therefore, the current in the coil at the instant the motor is turned on is 12A.
B. To find the current in the coil when the motor has reached maximum speed, we need to calculate the voltage across the coil again. This time, we need to subtract the back emf from the supplied voltage. The back emf is essentially a voltage opposing the power supply when the motor is running.
Using the formula V = I * R and rearranging it to solve for the current, we have: I = (V - back emf) / R.
Plugging in the values, we have: I = (120V - 70V) / 10 ohms = 50V / 10 ohms = 5A.
Therefore, the current in the coil when the motor has reached maximum speed is 5A.