Electric current:
The rate of flow of electric charge through any cross section is called electric current. Ampere is the SI unit of current.
Potential difference and emf:
Emf is the total amount of energy supplied by the battery or the cell in driving one coulomb of charge from its positive to the negative terminal through the battery.
Ohm's law:
The value of current I passing through a conductor is directly proportional to the potential difference V applied across its ends, provided the temperature and the physical state of the conductor does not change.
V I
V=IR
Resistance:
The property of a substance which opposes the flow of current through it is called its resistance. Its unit is ohm Ω
Effect of temperature on resistance:
Resistance is directly proportional to temperature. As temperature is increased, resistance increases.
Resistance thermometer:
Resistance thermometers, also called resistance temperature detectors (RTDs), are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers (PRTs
Galvanometer:
Galvanometer is a sensitive instrument used to detect current in a circuit. It is connected in a circuit in series.
Ammeter:
It is used to measure the current in a circuit. It is made with slight modification in galvanometer by using a shunt resistance in parallel with galvanometer. Ammeter is used in series in a circuit.
Voltmeter:
It is an instrument used to measure potential difference between two points. Galvanometer is converted to voltmeter by connecting a suitable resistance in series with it. Voltmeter is always connected in parallel with the circuit.
Joule's law:
The amount of heat energy generated in a resistance due to flow of electric current is equal to the product of the square of current, resistance and the time interval
W=I2Rt
Electric power:
The amount of energy supplied by current in unit time is known as electric power.
P=W/t
D.C and A.C:
The current which does not change its direction of flow is known as direct current (D.C).
A current which changes its direction of flow again and again is known as alternating current (A.C).
Fuse:
it is a small wire connected in series with the live wire. A specified value of current can safely pass through it. When the current passing through it exceeds this limit, it gets so hot that it melts and circuits break.
Circuit breaker:
It is a safety device which is used in place of fuse. Due to any fault when the current exceeds the safety limit, then the button of the circuit breaker moves upward. Due to which, the circuit breaks and the flow of the current stops in it.
Earth wire:
It connects electrical equipments directly to the earth. A connection to ground limits the voltage built up between power circuits and the earth, protecting circuit insulation from damage due to excessive voltage. Connections to ground limits the build-up of static electricity when handling flammable products or when repairing electronic devices.
Magnetic effect of electric current:
A current carrying conductor produces magnetic field around it in the form of concentric circles. The direction of magnetic field can be determined by right hand rule.
Force on a current carrying conductor in a magnetic field:
When a current carrying conductor is placed in a magnetic field, a force acts on the conductor. The direction of force can be determined by left hand rule.
According to this rule, stretch the thumb, forefinger and the middle finger of the left hand mutually at right angles to each other. It the forefinger points in the direction of the magnetic field, then middle finger in the direction of current and the thumb would indicate the direction of force acting on the conductor.
D.C motor:
When a current carrying coil is placed in a magnetic field, it experiences a couple due to which the coil begins to rotate. A D.C motor works on this principle. It converts electrical energy into mechanical energy.
Faraday's law of Electromagnetic induction:
When magnetic flux through a coil is changing, an emf is induced in it. The value of this induced emf is directly proportional to the rate of change of flux. This is known as Faraday's law of electromagnetic induction.
A.C generator:
An A.C generator consists of a coil. When this coil is made to rotate in a magnetic field, the magnetic flux through it continuously changes due to which an alternating voltage is induced in it.
Mutual induction:
If a change of current in a circuit induces a current in another circuit, this phenomenon is knows as mutual induction.
Self induction:
If the current through a coil or circuit changes and this changes induces an emf in the circuit itself, the phenomenon is knows as self induction.
When the switch is put on (see fig above), the bulb is not flashed as the voltage of battery is insufficient to turn it on. But when the switch is turned off, bubl flashes for a while which shows a higher voltage has been passed. This high voltage is the self induced voltage produced in the coil at the instant when the switch is put off.
Transformer:
Transformer is an electrical device which is used to increase or decrease the value of an alternating voltage.
