Electricity

A continuous and closed path of electric current.

Electric current is expressed by the amount of charge flowing through a particular area in unit time.

ampere, A

I=Q/t

Coulomb, C

an instrument for measuring electric current in amperes.

Q = It

charge in 6 X 10^18 electrons

-1.6x 10^-19 C

battery

Potential difference between two points in an electric circuit carrying some current is the work done to move a unit charge from one point to another.

W/Q (energy/charge)

V (Volt)

1J/C

A device used to measure voltage, or electrical potential energy difference

The potential difference, 'V' across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it provided the temperature remains the same

V = IR

The property of a conductor to resist the flow of charges through it.

Ω Ohm.

the current will be halved

A component used to regulate current without changing the source of the voltage.

A device which can vary the resistance without opening the circuit

Length, Area of cross section, Nature of its material

is retarded by its resistance. Low resistance, good conductor. High resistance, poor conductor.

An electrical device that resists the flow of electrical current due to its appreciable resistance.

p l/A

The electrical resistance of a conductor of unit cross-sectional area and unit length.

Ωm

V= V1 + V2 + V3

R= R1 + R2 + R3

Different appliances requiring different levels of current cannot be connected. If one component fails, the entire circuit breaks.

The reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances. 1/R = 1/R1 + 1/R2 + 1/R3

If one of the components fails, the others still work. Each component receives the required amount of current since they are in different branches.

If the electric current is purely resistive, the source energy gets dissipated in the form of heat.

P = VI

H = I^2Rt or VIt

The heat produced in a resistor is directly proportional to the square of current for a given resistance, directly proportional to the resistance for a given current and directly proportional to the time for which current flows through the resistor.

the emission of visible light by a hot object

temperature increases

Should have a high melting point, have high resistance and be thermally isolated

The rate at which electric current is dissipated or consumed in an electric circuit.

V^2/R or P = VI

W

1Vx 1A

1000W

1 watt of power for 1 hour

1000 watt x 3600 second or 3.6 x 10^6 J

VIt

Tungsten - highest melting point and high resistivity

Al, Cu, Fe alloy

Nichrome as it is an alloy, therefore has higher melting point, higher resistance and does not oxidise.

The voltage at which the appliance functions and the rate of consumption (power) of that voltage.

Joules (J)

Power x time

length, temperature

area of cross section