Answer: -60v
Step-by-step explanation:
As the given parameters are:
Applied voltage on DC shunt motor (V) = 250V
Armature resistance (R) = 2Ω
Armature current on full load (I1) = 40A
Armature current on no load (I2) = 10A
The back EMF (E) of a DC shunt motor can be calculated using the formula:
E = V - I * R
where V is the applied voltage, I is the armature current and R is the armature resistance.
When the motor is on full load, the armature current is I1 = 40A, so the back EMF can be calculated as:
E1 = V - I1 * R
E1 = 250V - 40A * 2Ω
E1 = 250V - 80V
E1 = 170V
When the motor is on no load, the armature current is I2 = 10A, so the back EMF can be calculated as:
E2 = V - I2 * R
E2 = 250V - 10A * 2Ω
E2 = 250V - 20V
E2 = 230V
Therefore, the change in the back EMF when the motor goes from full load to no load is:
ΔE = E1 - E2
ΔE = 170V - 230V
ΔE = -60V
Hence, the change in the back EMF when the applied voltage on the DC shunt motor is 250 volts, armature resistance is 2 ohms, armature current on full load is 40 ampers, and on no load 10 ampers are -60V.