Factors which influence the current induced in a solenoid are
➢ Number of turns
➢ Strength of barmagnet
➢ Relative speed of barmagnet or solenoid
Electromagnetic Induction
The direction of induced e.m.f is given by Fleming’s Right Hand Rule also known as generator rule
Note: factors on which direction of induced current depends
➢ Direction of magnetic field
➢ Direction of motion of the conductor
➢ Relative motion of the conductor and magnet.
Application of Electromagnetic Induction ➢ Generators
➢ Moving coil microphone
➢ Transformer
➢ Inductors
GENERATOR • Generator is a device which convert mechanical energy into electrical energy
• It will produce both AC and DC by using AC generators and DC generators
AC GENERATOR
Working When the armature coil rotates between the field magnets it will cuts magnetic flux and an e.m.f is induced in the armature coil by electromagnetic induction. This e.m.f will flow to the external circuits through slip rings and brushes.
For one complete rotation the direction of induced current will changes twice
The frequency of electricity generated in India is 50Hz
• 50Hz means the armature completes 50 rotations in 1 second
• The direction of current changes 100 times (50Hz)
• In order to overcome this practical difficulty, the number of rotations is reduced by increasing the number of armature coils and increasing the number of pole pieces
DC GENERATORS
Working When ever armature coil rotates between field magnet an e.m.f is induced in the armature coil by electromagnetic induction. After every half rotation the brushes B1 comes into contact with armature part moving upward and B2 comes into contact with armature coil moves downwards. So, the direction of current is same in each half rotation. Thus, split ring commutator will help to convert AC into DC
Note:
• By using split ring commutator, we can convert an AC generator into DC generator
Mutual Induction
When the switch is put ON and OFF only at that instant bulb will glow. Because the current is varying and varying magnetic flux will cause mutual induction
When the switch is still in ON position the bulb will not glow because DC is used here so current is constant, constant magnetic field is produced hence there is no mutual induction
When it is replaced by an AC source bulb will glow continuously, because varying magnetic flux will cause mutual induction
Transformer
➢ It is a device works on the principle of mutual induction
➢ Transformer will not work on DC it will works only in AC
➢ It used to increase or decrease the AC voltage / current
➢ There are two types of transformers step-up and step-down transformers.
Self-Induction
When both the switches are getting ON a varying magnetic field is developed around the coil in fig(b) because of AC, a back emf is induced in it due to self- induction, the resultant voltage across the bulb decreases hence brightness of the bulb decreases
• In fig (a) a DC source is used, there is no self-induction in DC circuit so brightness of the bulb is maximum
• When a soft iron core is inserted into the solenoid the magnetic flux linked with the coil also increases hence back emf become large it will further reduces the glow of bulb
Inductor
Inductors are widely used in AC circuits because they can control the amount of current in AC circuit without any power loss
• The advantage of inductor over resistor is that it will not have any energy loss in the form of heat while in resistors it will have power loss in the form of heat.
• Inductors are not used in DC because it will act as resistor in DC have energy loss
Moving Coil Microphone
Structure
The weak electrical signal from microphone is strengthened by using Amplifier
• The amplified signal is fed to loud speaker
Power Transmission and Distribution
• In India power is generated at power station in 11KV (11000V)
• When it is transmitted to distant places there is a loss of energy in the form of heat.
Q) How will you reduce the transmission loss?
Ans)
• by increasing the voltage up to 220KV the current flowing through the conductor is minimised hence, by joule’s law (H = I 2 Rt) heat loss can be reduced
• by increasing the thickness of the conductor
Q) if the current is reduced to half, how much will be the reduction in heat?
Ans) I = I/2 so heat, H = (I/2) 2 Rt = I 2 Rt/4 = H/4
Heat is reduced by four times
Note:
• in power stations step up transformers are used
in distribution transformer step down transformers are used
• in substations step down transformers are used
• the voltage between a phase line / live line and neutral line is 230V
• the voltage between a phase line / live line and earth is 230V
• the voltage between a phase line / live line and another phase line is 400V
• the voltage between a neutral line and earth is 0V
• a man standing on the earth touches the phase line will get electric shock
• a man standing on the earth touches a neutral line will not get electrocuted
• for a household electrification at least two lines are needed one is phase line and other is neutral line
Household Electrification
electrical line first reaches to the device kWh meter/ watt hour meter/ energy meter
• earth line starts from kWh meter
• watt hour meter is used to measure the amount of electrical energy consumption
• fuse wire is connected with phase line in series.
• Main switch will control/ regulate the current flowing into the household circuit
• Red colour- phase line, Green colour- earth line, Black colour- neutral line
• The earth wire is connected with E pin in the three-pin plug socket
• All the devices in household circuits are connected in parallel
Safety Measures in Household Electrification
1. Safety Fuse
