Unit 202 Revision #2

The relationship between the mass of a body (m), the applied force to the body (F) and the acceleration of the body (a) is given by the formula

• Force = mass x acceleration, F = m x a

• mass = Force x acceleration, m = F x a

• acceleration = mass x Force, a = m x F

• acceleration = mass / Force, a = m / F.

The SI unit of time is the second. Express 0.00001 seconds in a suitable sub multiple

• 10 milliseconds, 10 ms

• 100 milliseconds, 100 ms

In a magnetic circuit the magnetic field strength H is expressed in ampere turns/metre. H is calculated using the formula

The formula used to calculate the resistance (R) of a conductor, given its length (l), cross sectional area (a) and the constant of resistivity (r)

A simple alternator consists of a coil which is rotated in a permanent magnetic field.

      The emf generated in the rotating coil is connected to a load via the-

• commutator and brushes

• flexible cables

• slide rails and contacts

• slip rings and brushes

If the input energy and output energy of a machine are known, the percentage efficiency of the machine is calculated using the formula

The most common material used to manufacture brushes used in a.c. and d.c. rotating machines is

• Copper

• Carbon

• Aluminium

• Verulamium

The material used as an insulator on which overhead lines are suspended from pylons is

• Glass

• Mica

• PVC

• Rubber

Electric current is the flow of negatively charged particles called

• protons

• electrons

• neutrons

• atoms

In a domestic battery system linked to a PV installation the emf is produced by

• heating effect

• magnetic effect

• chemical effect

• movement effect