Ch 14 Flashcards
Electric current
Rate of flow of charges through any cross sectional area
I=q/t
Ampere
Conventional current
Current flowing from positive to negative terminal of a battery due to the flow of positive charges
Galvanometer
sensitive instrument that can detect small current in a circuit.A current of few milliamperes is sufficient to cause full scale deflection in it
Ammeter
After suitable modification galvanometer can be converted into ammeter a large current of the range as 1a or 10 a can be measured with ammeter
Potential difference
Potential difference across the two ends of a conductor causes the dissipation of electrical energy into other form of energy as energy flow through the circuit
Emf
It is the energy supplied by a battery to a unit positive charge when it flows through the closed circuit or a energy converted from non electrical form to electrical form when one coulomb of positive charge passes through the battery
E=w/q
Jc–¹
Unit of emf
If the emf of the battery is 2v the total energy supplied by the battery is 2j when one coulomb of charge flows through the closed circuit
Ohm law
The amount of current passing through a conductor is directly proportional to the potential difference applied across its ends provided the temperature and the physical state of the conductor does not change
V=I/R
Resistance
The property of a substance which offers opposition to the flow of current through
Ohm
Ohm unit
When a potential difference of one volt is applied across the ends of a conductor and one ampere of current passes through it then it’s resistance will be one ohm
Ohmic
Materials that obey ohm law and hence have a constant resistance over a wide range of voltages
Linear voltage current relationship
Metals
Non ohmic
Material having resistance that changes with change of current and voltage
Non linear voltage current
Filament lamp
Thermister
Parallel circuit advantages
Each device in the circuit receives the full battery voltage
Each device in the circuit may be turned off independently without stopping the current flowing to the other devices in the circuit
Joules law
The amount of heat generated in a resistance due to flow of charges is equal to product of square of current and distance R and time duration T
W=V²t/R
Electric power
The amount of energy supplied by current in unit time is known as electric power
I²R
Watt
Kilowatt hour
The amount of energy delivered by a power of one kilowatt in one hour is called kilowatt hour
3.6Mj
Dc
The current derived from a battery or cell is called direct current it is unidirectional
Positive and negative terminal have fixed polarity
Ac
The current that changes direction after equal intervals of time is called ac
Time period
The time interval after which the ac voltage or current repeats it’s value is known as time period
Earth wire
Connected to a large metal plate buried Deep in the ground near the house
Neutral wire
The other wire is maintained at zero potential by connecting it to the earth at the power station itself and is called neutral wire
Live wire
This wire provides the return path for the current the third wire is at a high potential
Fuse
A fuse is a safety device that is connected in series with live wire to protect the equipment when excess current flows it’s short and thin piece of metal wire that melts when large current passes through it
5A,10A
Fuse safety measure
Should have slightly more rating than the current which the electrical appliance will draw under normal conditions
Fuses should be connected in the live wire so that the appliance will not operate after fuse has blown
Switch off the main before changing any fuse
Circuit breaker
Safety device it disconnects the supply automatically if current exceed the normal value
