Electricity Test - 11

Tungsten (W) is exclusively used for making filaments of electric bulbs. Tungsten has a fairly good resistivity (5.20×10⁻⁸Ωm) at 20 degree C. Tungsten is ductile and can be drawn into thin wires. Thin wires offer high resistance, offer great heating effect and produces light (H = I²Rt). The thin wires of tungsten do not melt at high temperatures since the melting point of tungsten is very high (3380 degree C).

An ammeter is always connected in series in an electric circuit. It is likely to burn out if connected in parallel.

As a convention, the direction of flow of positive charge was taken to be the direction of electric current. The direction of flow of electrons is opposite to the direction of conventional current.

Electrical resistivity (also known as resistivity) is an intrinsic property of a material that quantifies how strongly a given material opposes the flow of electric current. Resistivity of a material varies with temperature. Resistivity of a conductor increases with increase in temperature. When a wire is stretched, its material remains the same and hence, the resistivity remains the same.

Nichrome is used for electric wire heater since it is an alloy of nickel, chromium, manganese and iron, and does not oxidise easily at high temperatures. It has a resistivity of 100×10⁻⁶Ωm

An ammeter has a low resistance since it is always connected in series in an electrical circuit. If it is connected in parallel, a high current will flow through it and it is likely to burn out.

The two ebonite rods rubbed on fur repel each other because the electrical properties of the two ebonite rods are similar to each other. Both the rods acquire like charges when rubbed on fur. Ebonite is a very hard rubber obtained by vulcanizing natural rubber for prolonged periods. The rods gain electrons when rubbed on fur and acquire negative charge.

A light bulb has a higher resistance. A toaster produces more heat than a light bulb since it draws a higher current from the same source when connected in parallel. According to Joule's law of heating, the heat produced in a resistor is directly proportional to the square of the current for a given resistance, directly proportional to the resistance for a given current and directly proportional to the time for which the current flows through the resistor. H = I²Rt.