Random 1
2000V is converted to 100V
Identify the type of transformer present
Step down transformer
Give the term
The effect of a force that causes rotation.
Torque
Occurs when a current carrying conductor inside a magnetic field experiences a force.
M____________
Which of the following represents the formula for TORQUE?
= ILB Cos Ꝋ
= nI AB Sin Ꝋ
= nI AB Sin Ꝋ
Which of the following is NOT a formula for acceleration?
a = F/m
a = Eq/m
a = E x m/q
a = v - u /t
a = E x m / q
A transformer built in a radio reduces the 240V supply voltage to 12V.
If the number of turns in the secondary coil is 100 what is the number of primary coils?
NP /NS = VP /VS
NP = VP x NS / VS
NP = 240 x 100 / 12
NP = 2000 turns
Which motor has a
Split ring
Slip ring
Split ring = DC
Slip ring = AC
qE = qvB
Identify
(q)
(E)
(B)
q = charge
E = Electric field
B = Magnetic field strength
When the north pole of a magnet is moved into a coil the direction of the induced current in the coil as seen from the magnet side is ______________.
Use the right-hand rule
Anticlockwise
Identify the scientist who produced the first DC motor.
Michael Faraday
A student places a square coil of wire with a side length of 5cm in a uniform VERTICAL magnetic field of strength 0.1T.
The plane of square is at an angle of 400 to the magnetic field.
Calculate the magnetic flux.
A = (0.05 x 0.05) = 0.0025
= 0.1 x 0.0025 Cos 40
= 1.9 x 10^-4 Wb
Name of the device which transforms mechanical energy into electrical energy.
Generator
Give the name of the law
An induced current produces magnetic fields which tend to oppose the change in magnetic flux that induces such currents.
Lenz Law
A uniform electric field is set up between two parallel plates 5 cm apart, with a potential difference of 120 V between the plates.
Calculate the magnitude of the electric field.
E = V/d
E = 120/0.05
E = 2400 V/m
Using the formula
B = E/v
Calculate the magnetic field strength given the electric field is 2 V/m and the velocity is 3m/s
B = 2 / 3
B = 0.67 T
A radio with 2000 turns in the primary coil and 100 turns in the secondary coil draws current 4A.
What is the current in the primary coil.
IP /IS = NS /NP
IP = NS x IS / NP
IP = 100 x 4 / 2000
= 0.2A
Identify the part of a DC motor that changes the direction of the current every half rotation in order to keep the coil motion continuous
Split ring
A single square coil wire with side lengths of 5cm is free to rotate within a magnetic field with strength 1 x 10^-4 T.
A current of 1A is flowing through the coil.
ꚍ = 1 x 1 x 0.0025 x (1x10^-4) Sin 90
ꚍ = 2.5 x 10^-7 Nm
A conductor enters a constant magnetic field.
Describe the conductor as it enters the loop
Describe the conductor as it exits the loop
Entry = current has a non zero magnitude
= generates a magnetic field that opposes
the change in flux
Describe what happens when a bar magnet enters a conducting loop.
As the bar magnet approaches the loop, it experiences a repulsive force due to the induced emf.
Since like poles repel, the loop must behave as if it were a bar magnet with its north pole pointing up.
Two parallel plates are separated by 1cm. One plate is earthed the other has a potential of 5kV.
Determine the final speed of an electron (v)
v2 = 2qv / m
v2 = 2(1.6 x 10^-19 x 5 x 10^3) / 9.1 x 10^-31
v2 = 1.7 x 10^15
v = 4.2 x 107 m/s
Indicate how the speed of a DC motor can be controlled.
An electron travels with a velocity of 3400 m/s at an angle of 60° to the horizontal and enters an electric field of magnitude 1200 N/C .
Calculate the acceleration of the electron.
F = ma = Eq
a = Eq/m
a = 1200 (1.602 x 10^-19) / 9 x 10 ^ -31
a = 2.136 x 10^14 m/s/s
Calculate the force on the conductor given;
The conductor has a length of 1.2m and carries 4A at angle of 40o to the magnetic field which is 2T.
F = I x L x B x Sin (pheta)
F = 4 x 1.2 x 2 Sin (40)
F = 6.17 N
Calculate the work done in joules for a proton between two parallel plates that are 3m apart and experience a unform electric field of 200 V/m.
W = q x E x d
W = (1.6 x 10^-19) x 200 x 3
W = 9.6 x 10 ^-17