Electricity

Efficiency of Electrical Appliance The efficiency of an electrical appliance is given by the following equation Normally, the efficiency of an electrical appliance is less than 100% due to the energy lost as heat and the work done against friction in a machine. Example 1A lamp is marked “240V, 50W”. If it produces a light … Read more

Power Rating Figure above is an example of power rating label. An electrical appliance which is marked 240V, 1200W means that the electrical appliance will consume 1200J of energy in every second if the potential difference across it is 240V. ExampleA bulb rated 240V/80W is operated from a 120V power source. Find the resistance and … Read more

In a circuit of any connection (series or parallel), the power dissipated in the whole circuit is equal to the sum of the power dissipated in each of the individual resistor. Example 1:2 identical bulb of resistance 3Ω is connected to an e.m.f. of 12V. Find the power dissipated in the circuit ifa. the bulb … Read more

Power The electric power, P is defined as the rates of energy that supply to the circuit ( or the rates of work been done ) by sources of electric. The unit of electric power is the watt (W). One watt of power equals the work done in one second by one volt of potential … Read more

Electrical Energy From the definition of potential difference, the electrical work done is given by the equation W=QVWhereW = workQ = chargeV = potential difference Since the work done must be equal to the energy to do the work, therefore we can also say that the electrical energy ( E ) is also given by … Read more

Measuring e.m.f. and Internal Resistance Three methods can be used to measure the e.m.f. and internal resistance. Open circuit-Close circuit Simultaneous equation Linear Graph Open Circuit – Closed Circuit Open CircuitIn open circuit ( when the switch is off), the voltmeter shows the reading of the e.m.f.Close CircuitIn close circuit ( when the switch is … Read more

Internal Resistance The internal resistance of a source (cell or generator) is the resistance against the moving charge in the source. Load Resistance The load resistance in a circuit is the effective resistance against the moving charge outside the source of electric. Terminal Potential Difference The terminal potential difference or terminal voltage is the potential … Read more

Electromotive Force Potential Difference Similarities:Have same unit (Volt)Can be measured by Voltmeter DefinitionThe electromotive force (e.m.f.) is defined as the energy per unit charge that is converted from chemical, mechanical, or other forms of energy into electrical energy in a battery or dynamo. DefinitionThe potential difference (p.d.) between two points is defined as the energy … Read more

Electromotive Force In a circuit, the electromotive force is the energy per unit charge converted from the other forms of energy into electrical energy to move the charge across the whole circuit. In equation,where E = e.m.f.,W = energy converted from non-electrical forms to electrical formQ = positive charge. The unit of e.m.f. is JC-1 … Read more