Force
Identify the unit for force.
Newton (N)
Electric fields are exerted by
a) Magnets
b) Current carrying conductors
B
Where do we find transformers?
Appliances
Transmission towers
Distinguish between an AC and DC motor
AC uses alternate current and contains slip rings
DC uses direct current and contains split rings
Give the name of the scientist who moved a magnet in and out of a coil of wire and produced electric current.
Far_________
Faraday
Give the FORCE calculation for the following;
an electron with a mass of 9.109 x 10^-31 kg accelerates 0.24m/s/s.
F = m x a
What are the units for electric field strength?
N/m
N/C
Outline the function of a transformer.
If the voltage is 120V and the current is 2A. Calculate the power.
P = VI
P = 120 x 2
P = 240 Watts
Give the FORCE formula for a conductor that is perpendicular to the magnetic field.
F = n x I x L x B
Calculate the electric field strength for two parallel plates that are separated by a distance of 20cm and experiences a voltage 30V
E = V/d
E = 30/0.2
E = 150 V/m
VP/VS = NP/NS
Transformers consist an iron core containing coils of wire.
If the number of coils in the primary transformer is 200 turns and the 600 turns in the secondary transformer which experiences a voltage of 50V.
Calculate the voltage in the primary transformer.
VP = VS x NP / NS
= 50 x 200 / 600
= 17 V
Calculate the torque for a loop with an area of 4m2 within a magnetic field 0.3T. The loop experiences 3A of current.
The angle between the loop and magnetic field is 50o
Torque = nBIA Cos (pheta)
= 1 x 0.3 x 3 x 4 Cos 50
= 2.31 N/m
Calculate the power lost in transmission lines given the current is 30A and the resistance is 10 ohm.
P = I2 R
P = 302 x 10
P = 9000 Watts
Calculate the force on a current carrying conductor which has 2A and a length of 3m. The conductor experiences a magnetic field of 4T.
F = n x I x L x B
= 1 x 2 x 3 x 4
= 24N
Calculate the distance between two plates given the electric field strength is 2000 V/m and the supply voltage is 40V.
E = V/d
d = V/E
d = 40 / 2000
d = 0.02
d = 2cm
VP/VS = NP/NS
Transformers consist an iron core containing coils of wire.
If the number of coils in the primary transformer is 1000 turns and the 500 turns in the secondary transformer which experiences a voltage of 20V.
Calculate the voltage in the primary transformer.
Indicate if it is a STEP UP or STEP DOWN transformer.
VP/VS = NP/NS
VP = NP x VS/NS
VP = 1000 x 20 / 500
VP = 40V
Step down transformer
Calculate the torque for a square loop with a side length of 5m within a magnetic field 0.3T. The loop experiences 2A of current.
The angle between the loop and magnetic field is 50o
Torque = nBIA Cos (pheta)
= 1 x 0.3 x 2 x (5 x 5) Cos 50
= 9.64 N/m
What is the function of
Slip rings
Split ring
Slip ring = electrical contact between input AC and motor coil.
Split ring = deliver DC to external unit.
Calculate the force on a current carrying conductor which has 5A and a length of 3m. The conductor experiences a magnetic field of 4T.
The angle between the conductor and magnetic field is 30o.
F = n x I x L x B Sin (pheta)
F = 1 x 5 x 3 x 4 Sin 30
F = 30N
Two plates are separated by a distance of 10cm.
Calculate the electric field strength given the current and resistance on the plates is 2A and 4 ohm.
V = I x R
V = 2 x 4 = 8V
E = V/d
E = 8 / 0.1 E = 80 V/m
VP/VS = NP/NS
Transformers consist an iron core containing coils of wire.
If the number of coils in the secondary transformer is 500 turns which experiences a voltage of 20V. The primary transformer experiences 120V.
Calculate the primary turns.
VP/VS = NP/NS
NP = VP x NS / VS
NP = 120 x 500 / 20
NP = 3000 turns
How is an emf produced?
Occurs when there is movement between a conductor and a magnetic field.
Distinguish between motors and generators
Generators convert mechanical energy into electrical energy.