4TE2_Recall Ex

Earthing - How is an electrical appliance earthed and how does earthing protect the user?

Answer explanation

Earth wire is connected to metal casing of appliance.

It provides a low resistance path for charges to earth, preventing charges frm traveling through the user.

State Ohm's law

Answer explanation

It states that the current through a metallic conductor is proportional to the p.d. applied across its ends, provided physical conditions like temperature are kept constant.

State a use for the following e.m. waves:

(1) infra-red

(2) ultraviolet

Answer explanation

Infra-red: Intruder's alarm, tv remote control

UV: Disinfection of medical equipment

State two properties of e.m. waves

Answer explanation

1) They are transverse waves.

2) They travel at 300 000 000 m/s through vacuum.

State what is meant by wavefront

Answer explanation

It is an imaginary line that connect adjacent points on waves that are in phase.

State the principle of conservation of energy

Answer explanation

Energy cannot be created or destroyed

but it can be converted from one form to another

o transferred from one body to another

the total energy in an isolated system is constant

State the principle of moments

Answer explanation

At equilibrium,

the sum of the clockwise moment about a pivot is

equal to the sum of the anticlockwise moment about the same pivot

State what is a gravitational field

Answer explanation

It is a region where a mass experiences a gravitational force.

State what is meant by constant acceleration

Answer explanation

It means that the change in velocity per unit time is the same.

Explain what is a critical angle

Answer explanation

It is the angle of incidence in the optically denser medium when the angle in the optically less dense medium is 90 degrees.