Electric line testor is used for testing alternating current (AC). In an electric line, ‘phase’ line gives out AC which has both positive and negative components. Usually when current is allowed to pass through a bulb from the ‘phase’ to ‘neutral’, which is at lower potential, the bulb glows.
In the case of a testor, when we touch its metal cap, a very small amount of current being tested passes through the neon bulb, a high resistance and through the body to the earth which is at zero potential.
In other words the body helps to complete the circuit enabling the testor to glow. The high resistance inside the testor acts as a safety mechanism by restricting the amount of current passing through the body.
