Science [2 Mark Questions]

V =220V, I = 0.5amp, P = ?
We know that
P = VI = 220 × 0.5
P = 110 watt.

When an electric current is passed through a high resistance wire, the wire becomes very hot and produces heat. This effect is knows as heating effect of current. This effect is used in room heaters and electric ovens.

Conductors: Those substances through which electricity can flow are known as conductors.E.g., Copper, silver etc.
Insulators: Those substances through which electricity cannot flow are known as insulators.
E.g., Plastic, cotton etc.

The connecting wires of the heater get only slightly warm because they have extremely low resistance due to which negligible heat is produced in them by passing current.

If air is filled in an electric bulb, then the extremely hot tungsten filament would burn up quickly in the oxygen of air. So, the electric bulb is filled with a chemically unreactive gas like argon or nitrogen. Thes gases do not react with the hot tungsten filament and hence prolong the life of the filament of the bulb.

Tungsten is used for making the filaments of electric bulbs because it has a very high melting point. Due to its very high melting point, the tungsten filament can be kept white hot without melting away. Also, tungsten has high flexibility and low rate of evaporation at high temperature.

The two lamps (of 4V each) should be arranged in parallel with the two 2V cells.

I = 0.36A, t = 15min = 900 seconds.
Q = I × t
= 0.36 × 900
= 324C.

1. Turn the switch to right side so as the resistance decreases.
2. Turn the switch to the left side so as the resistace increases.

If we take two similar wires of same length and same diameter, one of copper metal and other of nichrome alloy, we will find that the resistance of nichrome wire is about 60 times more than that of the copper wire. This shows that the resistance depends on the nature of material of the conductor.

When 1 coulomb of charge flows through any cross-section of a conductor in 1 second, the electric current flowing through it is said to be 1 ampere.

Copper has free electrons that are loosely held by the nuclei of the atoms. These free electrons result in conduction of electricity. The electrons present in rubber are strongly held by the nuclei of its atoms. So, rubber does not have free electrons to conduct electricity.

Silver and copper are good conductors of electricity because they have free electrons available for conduction.

Because,

1. Resistivity of an alloy is much higher than that of a pure metal.
2. An alloy does not undergo oxidation (or burn) easily even at high temperature.

I = 200mA = 0.2A
R = 4 × 103ohm = 4000 ohm
We know that
V = IR
V = 0.2 × 4000
V = 800 volt.

Given: V = 230V, I = 0.4 amp
Rate at which electric energy is transformed = Power
Power = V × I
= 230 × 0.4
= 92W = 92J/s

I = 6 amp, R = 40 ohm
We know that
V=IR
V = 6 × 40 = 240V.

One watt hour is the amount of electrical energy consumed when an electrical appliance of 1 watt power is used for 1 hour.
1 watt hour = 3600 joules.

Parallel circuits – Because if one electrical appliance stops working due to some defect, then all other appliances in the circuit will keep working properly.

Conventional direction of flow of electric current is from positive terminal of a battery to the negative terminal, through the outer circuit. The direction of flow of electrons is opposite to the direction of conventional current, i.e. from negative terminal to positive terminal.

1. By increasing the area of cross section, the resistance will decrease.
2. By increasing the diameter, the resistance will decrease.

The electric potential (or potential) at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.Unit of electric potential is volt.

I = 5amp, V = 220 Volt, t = 2h
P = ?, E = ?
P = V × I
= 220 × 5
= 1100 watt
= 1.1KW
Energy consumed, E = P × t
= 1.1 × 2
= 2.2KWh

Electric current is the flow of electric charges (electrons) in a conductor such as a metal wire.
SI unit of electric current is ampere.

1. A long piece of nichrome wire.
2. A thin piece of nichrome wire.

When an electrical appliance consumes electrical energy at the rate of 1 joule per second, its power is said to be 1 watt.
1 watt = 1 volt × 1 ampere.

According to the law of combination of resistances in series, the combined resistance of any number of resistances connected in series is equal to the sum of the individual resistances.

The rate at which electrical work is done or the rate at which electrical energy is consumed is known as electrical power.
It is given by P = VI = Watt
P = VI = Watt

Given: V = 3V, I = 0.5 amp

1. R = ?

we know that V = IR

3 = 0.5R

R = 6 ohms

2. Power of lamps = VI

3 × 0.5

= 1.5 watt