Physics [2 Mark Question Answer]

The fuse helps to control the maximum current in an electrical circuit. The fuse protects an electrical circuit by melting and breaking the circuit, whenever the current exceeds the pre-determined limit in the circuit. Due to low melting point, the fuse wire melts and then breaks the circuit.

We know that, E =Pt
Given, P = 60 W= 0.06 kW
and, t = 50 hours
.·. E=0.06 x 50=3kWh

Watt-hour is the commercial unit of electrical energy.
One watt-hour is the electrical energy consumed by an electrical appliance of power 1 watt when it is used for 1 hour.
1Wh = 3600 J

The obstruction offered to the flow of current by the wire is called its electrical resistance. It is a kind of friction between the free electrons and the atoms of the conductor along which they flow.
Its SI unit is 'ohm'.

According to Ohm's law, the current flowing in a conductor is directly proportional to the potential difference across its ends provided the physical conditions and temperature of conductor remains constant.
No, it is not always true. E.g. Diode valve, junction diode etc. do not obey Ohm's law.

In the given diagram, ammeter is connected in parallel and voltmeter in series, which is wrong. Also the terminals of the two devices are wrongly connected to the battery.
Correct diagram:

An electrical circuit is a continuous path comprising of conducting wires and resistances between the terminals of a battery, along which an electric current is set up. It is represented by drawing a circuit diagram.

An electric cell is a device in which a constant difference in potential is maintained between the two conductors by a chemical reaction. Thus, a cell can be used as a source of electrons or current. In a cell, chemical energy changes into electrical energy when it is in use.

The instrument used to measure electric potential or potential difference is called a voltmeter. It has a very high resistance and is always connected in parallel.

At constant temperature, if current is plotted against potential difference, the plot will be a straight line making some slope with the x-axis as shown in figure below:

Two uses of conductors:
(i) Connecting wires are made of conductors like copper.
(ii) Conductors are used as electrolytes in cells

Ohm's law relates the current in a conductor to the potential difference across its ends.
According to Ohm's law, the current flowing in a conductor is directly proportional to the potential difference across its ends provided the physical conditions and temperature of conductor remains constant.

Let the required potential difference be V
Given, current I = 1 A and Resistance, R = 5 Ω
AIC to Ohm's law,
V = IR= (1) x (5) = 5 volt

Electric intensity is defined as the force experienced by a unit positive charge when kept at that point.
Its SI unit is newton per coulomb. It is a vector quantity.

To get a total resistance less than 2 ohm, the given resistors should be connected in parallel because in parallel combination the equivalent resistance is less than the resistance smallest connected resistor.

The rate of movement of charge from one point to another through a section of the conductor is called electric current. Current refers to rate of flow of charges in a conductor.
I = Q/t

Superconductors: Substance whose resistance decreases tremendously with the decrease in temperature and reaches nearly zero around absolute zero temperature are named as superconductors; e.g. lead, tin etc.

Semiconductors: Substances whose resistance decreases with the increase in temperature are named as semiconductors. E.g. manganin, constantan etc.

Electromotive force: When no current is drawn from a cell, when the cell is in open circuit, the potential difference between the terminals of the cell is called its electromotive force (or e.m.f.).

(i) Coulomb: It is the unit of charge.
(ii) Ohm: It is the unit of resistance. The resistance of a conductor is said to be 1 ohm, if 1 ampere current flows through it, when the potential difference across its ends is 1 volt.

Potential difference: The potential difference between two points may be defined as the work done in moving a unit positive charge from one point to the other.