Science [2 Mark Questions]

According to the law of combination of resistance in parallel, the reciprocal of the combined resistance of a number of resistances connected in parallel is equal to the sum of the reciprocals of all the individual resistances.

Silver metal.

I = 13 amp, V = 230V
Power = VI
= 230 × 13
= 2990W
P = 2.99KW

Nichrome alloy is used for making the heating elements of electrical appliances because:

1. Nichrome has very high resistivity.
2. Nichrome does not undergo oxidation (or burn) easily even at high temperature.

For obtaining 250 ohms, connect two 100 ohm in series with a parallel combination of two 100 ohms.

1. In case of series connection, if filament of one lamp breaks, the other wil stop glowing.
2. In case of parallel connection, if filament of one lamp breaks, the other will keep glowing.

The connecting cord of the heater made of copper does not glow because negligible heat is produced in it by passing current (because of its extremely low resistance); but the heating element made of nichrome glows because it becomes red-hot due to the large amount of heat produced on passing current (because of its high resistance).

Parallel arrangement because if one electrical bulb stops glowing due to some defect the other will keep glowing. Parallel arrangement takes more current from the battery due to its lesser equivalent resistance.

Conductor: Mercury, Aluminum, Iron, Metal Coin.
Resistor: Manganin, Nichrome.
Insulator: Rubber, Polythene, Wood, Bakelite, Paper, Thermocol.

An electric currrent is a flow of electric charges (electrons) through a conductor. Potential difference between the ends of the wire makes electric current to flow in the wire.

A series arrangement is not used for connecting domestic electrical appliances in a circuit because if one electrical appliance stops working due to some defect, then all other appliance also stop working as the whole circuit is broken.

Resistance of a conductor depends on the following factors:-
Length of the conductor, area of cross section of the conductor, nature of material of the conductor and temperature of the conductor.

Given: Potential difference = 12V, Charge moved = 1CWe know that,
Work done = Potential difference × charge moved
= 12 × 1 = 12 joules
Since work done on each coulomb of charge is 12 joules, the energy given to each coulomb of charge is also 12 joules.

V = 220V, P = 2.2kW = 2200W, t = 3h
We know that
Electrical energy consumed = P × t = 2.2 × 3 = 6.6kWh
We have, P = V × I
2200 = 220 × I
I = 10amp

Resistivity is the characteristic property of a substance which depends on the nature of the substance and its temperature. It is numerically equal to the resistance between the opposite faces of a 1m cube of the substance.

Resistivity of a substance on the nature of the substance and its temper. it does not depend the length or thickness of the conductor.

Conductor: Silver, Copper, Aluminum, Nichrome, Graphite, Mercury, Manganin.Insulators: Sulphur, Cotton, Air, Paper, Porcelain, Mica, Bakelite, Polythene.

1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to its ends, a current of 1 ampere flows through it.