Thanks! 1. A proton with a speed of 4.5 x 10^6 m/s is observed to travel in a ci
ID: 1394348 • Letter: T
Question
Thanks!
1. A proton with a speed of 4.5 x 10^6 m/s is observed to travel in a circle of radius 0.22m in a magnetic field. What is the strength of the magnetic field?
A. 2.3 x 10^-2 T
B. 2.1 x 10^-1 T
C. 4.7 T
D. 1.1 x 10^5 T
2. A 56V DC motor draws a 2.0A when running at full speed. If the resistance of the armature is 1.5 ohms, what is the back emf (reverse voltage) at this speed?
A. zero
B. 3.0 V
C. 53 V
D. 59 V
3. An ideal transformer is being designed to change a 640 V AC into 120 V AC. What should be the ratio of the number of turns on the primary coil to the number of turna on the secondary coil?
A. 0.035
B. 0.19
C. 5.3
D. 28
Explanation / Answer
as we know magnetic force is given by:
force=q*v*B
where q is charge
v is speed
B is magnetic field strength
this force will be balanced by the centripetal force
so mass*v^2/radius=q*v*B
then putting different values, we get B=0.213 T=2.1*10^(-1) T
hence option B is correct.
Q2.
as we know for a DC motor, if termianl voltage is Vt and back emf is Eb,
then
Vt=Eb+armature ressitance*current
56=Eb+1.5*2
Eb=53 volts
option C is correct.
Q3.as we know ratio of voltage=ratio of turns
hence
ratio of turns=640/120=5.33
hence option C is correct.
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