Amotor contains a coil with a total resistance of 13 and is

Amotor contains a coil with a total resistance of 13 and is supplied by a voltage of 120 V. When the motor is running at its maximum speed, the back emf is 66 V (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) Find the current in the coil at the instant the motor is turned on. Conceptualize Think about the motor just after it is turned on. It has not yet moved, so there is no back emf generated. As a result, the current in the motor is high. After the motor begins to turn, a back emf is generated and the current decreases Categorize We need to combine our new understanding about motors with the relationship between current, voltage, and resistance in this substitution problem. (B) Find the current in the coil when the motor has reached maximum speed Finalize The current drawn by the motor when operating at its maximum speed is significantly less than that drawn before it begins to turn. What if we want to keep the power input under 3.1 times the power when it is at maximum speed to prevent overheating? (a) What is the minimum back emf (in volts) required to keep the power input at the desired level? Follow the example closely. What are the two currents that we want to compare? Your response differs significantly from the correct answer, Rework your solution from the beginning and check each step carefully (b) Let us denote as the motor\'s angular speed that gives the back emf found in part (a), andbe the maximum angular speed of the motor. Find the ratiko How is the angular speed related to the back emf? Your response differs from the correct answer by more than 100%.

Solution

1.

current is calculated as follows:

    I = E/R = 120 / 13 = 9.23 A

Current is calculated as follows:

I = E - e /R = [120 - 66]/ 13 = 4.15 A