Table of contents | |
The Motor Effect | |
Fleming’s Left Hand Rule | |
Electric Motor | |
Magnetic Flux Density | |
Electromagnetic Induction | |
Dynamo / DC Generator | |
Transformers | |
National Grid |
As the sides of the coil experience opposite forces, the coil will rotate. The coil is connected to the circuit using brushes and a split-ring commutator. The brushes allow electricity to be conducted to the coil while also allowing it to move. The split-ring ‘breaks’ and re-connects the circuit every half turn to allow constant rotation.
Electric motors can be made more powerful by:
F = B I L
F = force (N
B = magnetic flux density (Tesla, T)
__I __= current (A)
L = Length (m)
Solved Example
A wire has a current of 2.2A flowing through it as it passes through a magnetic field of 0.5T. What force will the 0.25m wire experience?
F=BIL
F = 0.5 x 2.2 x 0.25
F = 0.275N
When a wire is moved through a magnetic field, electric current is induced in the wire
Alternator
Electricity can be generated by rotating a magnet inside a coil of wire. This induces a current in the wire. As the magnetic field is changing direction repeatedly (as it turns), the direction of the induced current also changes. Therefore, alternating Current (AC) is produced. This type of generator is called an alternator.
An alternating current in the primary coil creates an alternating magnetic field around the iron core. The secondary coil is in the alternating magnetic field. This induces an alternating current in the secondary coil. Transformers do not work with DC as the magnetic field does not change.
The relationship between voltage and the number of turns on the primary and secondary coil can be described using this equation (you do NOT need to remember this equation for your exam):
V = voltage
N = number of turns
P = primary coil
S = secondary coil
Solved Example
A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920V.
Vp/Vs = Np/Ns
920/Vs = 200/50
Vs = 920/4
Vs = 230V
Vp x Ip = Vs x Is
V = voltage
I = current
P = primary coil
S = secondary coil
Solved Example
A transformer is used to step down an alternating voltage of 230V to 12V for a 2.5A light bulb. Assume that the transformer is 100% efficient and calculate the current in the primary coil of the transformer.
Vp = 230V
Ip = ?
Vs = 12V
Is = 2.5A
230 x Ip = 12 x 2.5
Ip = (12 x 2.5) ÷ 230 = 0.13A
Every power station feeds into the grid and every consumer takes electricity from the grid. Transformers are used to step up voltage from power station to the grid and to step down voltage from the grid to homes (230V)
High voltages are used between pylons (400,000 V) so that less energy is lost (high voltage = low current at constant power [P=IV])
124 videos|149 docs|37 tests
|
|
Explore Courses for Grade 10 exam
|