Flux, velocity, current, power A wire was made into a square loop of side 0.15m
ID: 1314228 • Letter: F
Question
Flux, velocity, current, power
A wire was made into a square loop of side 0.15m is having a magnetic field (B) of 2.5-T. What are the maximum and minimum values of flux that can pass through the loop? 2. As we discussed in class that our blood has charged ions and this is how the rate of blood flow in our body's vessel can be measured. Pretend that the blood vessel is 0.002m in diameter, and the magnetic field is 0.080 T, and the measured emf is 0.10 mV. What is the flow velocity of the blood? 3. A DC Motor has armature windings with a resistance of 5.0 Q. The motor is connected to a 120-V line, and when the motor reaches full speed against its normal load, the back emf is 108V. Calculate (a) the current into the motor when it is just starting up, and (b) the current when the motor reaches full speed. 4. A portable radio cannot handle your home voltage of 120-V ac. So it uses a step-down transformer that changes 120-V ac to 9.0-V ac (Such a device also contains diodes to change the 9.0 -V ac to dc, to be like its 9.0-V battery). The primary coil contains 400 turns with a current of 0.030A. Calculate (a) the number of turns in the secondary coil, (b) the current in the secondary, and (c) the power transformed.Explanation / Answer
1. Flux = Magnetic field(B) * Area
= 2.5*0.152 = 0.05625 Weber
So maximum flux = 0.05625 W
Minimum flux = 0
2. Flow velocity = EMF/(Field*Area)
= 0.1*10-3/(0.08*0.0022*pi/4) = 397.88 m/s
3. Starting current = Voltage/Resistance = 120/5 = 24 A
Current in full speed = (V-BE)/R = (120-108)/5 = 2.4 A
4. a) No of secondary coils = 9/120*400 = 30
b) Current in secondary = 9/120*0.03 = 0.00225 A
c) Power = VI = 120*0.03 = 3.6 W