Ch15 Flashcards
Electromagnetism
Study of magnetic effects of current
Right hand grip
Grasp a wire with your right hand such that your thumb is pointed in the direction of current then curling fingers of your hand will point in the direction of the magnetic field
Solenoid
A coil of wire consisting of many loops is called a solenoid
Electromagnet
The type of temporary magnet which is created when current flows through a coil is called electromagnet
Right hand to find direction
If we grip a coil with our right hand by curling our fingers in the direction of the conventional current our thumb will indicate the north pole of coil
Fleming left hand
Stretch the thumb,forefinger,and the middle finger of the left hand mutually perpendicular to each other if the forefinger points in the direction of the magnetic field,the middle finger in the direction of the current then the thumb would indicate the direction of the force acting on the conductor
Armature
In a practical electric motor the coil called the armature is made of many loops mounted on a shaft or axle
Strength of magnetic field
Defined as the number of magnetic lines of force passing through any surface
Electromagnetic induction
The process of generating an induced current in a circuit by changing the number of magnetic lines of force passing through it
Faraday’s law
The value of induced EMF in a circuit is directly proportional to the rate of change of number of magnetic lines of force through it
Factors of induced emf
Speed of relative motion of the coil and the magnet
Number of turns of coil
Lenz law
The direction of an induced current in a circuit is always such that it opposes the cause that produces it
Mutual induction
The phenomenon of production of induced current in one coil due to change of current in a neighbouring coil
Transformer
Used to increase or decrease ac voltages
Step up transformer
If the secondary voltage is larger than the primary voltage the transformer is step up
Step down transformer
If the secondary voltage is smaller than primary voltage
Ideal transformer
The electric power delivered to the secondary circuit is equal to he power supplied to the primary circuit.this transformer dissipates no power itself
Relay
Is used to control a large current with the help of a small current relay is an electrical switch that opens and closes under the control of another electrical circuit
Thermionic emission
Process of emission of electrons from hot metal surface
Electron gun
Used to investigate the properties of electron beam
Cro
The cathode ray oscilloscope is an instrument which is used to display the magnitude of changing electric current or potentials
Analogue quantities
The quantities whose values vary continuously or remain constant
Analogue electronics
The branch of electronics consisting of circuits which process analogue quantities
