Introduction
Welcome to this section of your course, which introduces you, the learner to the topics of power and energy. There is a subtle difference between power and energy, which must be understood.
Objectives
By the end of this unit you will be able to:
· Understand the terms work, power and energy
· Calculate the power dissipation of various circuits
· Calculate the energy consumption of various circuits
· Measure power using an ammeter and a voltmeter
· Decide rating of resistors by physical size or marking
· Calculate the power dissipated in a series circuit
· Calculate the power dissipated in a parallel circuit
· Calculate the power dissipated in a series-parallel circuit
· Calculate the energy consumed by a load in a given time
· Understand how energy consumption is measured
· Calculate the cost of energy consumed, given meter readings
Reasons
An electrician must be able to decide the power consumption of electrical equipment in order to be able to install it correctly and to successfully locate faults.
Work and Force
Whenever a force of any kind causes motion, work is said to be done. When a mechanical force, for instance, is used to lift a weight through a distance, work is done. The SI unit of force is the Newton ( N ) and the unit of distance or length is the metre ( m ).
Work
Work is measured in terms of distance moved by the object and the force, which caused the movement.
Example:
A force of 4000 Newtons is required to lift a bundle of steel conduit through a distance of 2.5 metres. How much work is done in lifting the conduit?
