Physics [2 Mark Question Answer]

It means that if the bulb is lighted on a 250 V supply, it consumes 100 W electrical power (which means 100J of electrical energy is converted in the filament of bulb into the light and heat energy in 1 second).

(a) Terminal voltage is less than the emf : Terminal Voltage < e.m.f.
(b) e.m.f. is equal to the terminal voltage when no current is drawn.

Potential at a point is defined as the work done in bringing a unit positive charge from infinity
to that point. Its S.I. unit is volt, where 1 V = 1 joule/1 coulomb

The potentials of the two conductors determine the direction of flow of electrons. The electrons flow from the conductor at low potential to the conductor at high potential.

The resistivity of a substance is the resistance of a wire of that substance of unit length and unit area of cross-section. Its S. I. unit is ohm × m. An insulator will have higher resistivity.

The resistance of connecting wires should be almost negligible. For this thick wires are used . since a thicker wire has a small resistance and the wires are made of copper because the resistivity of copper is low.

Bends in the wire will not affect its resistance. This is because the electrons are extremely small in size as compared to the bends. So, the electrons can easily change their direction of motion.

When a given metallic wire is doubled on itself, its length is reduced to half, but its area of cross-section gets doubled. So, the resistance of the wire will become one-fourth i.e., the new resistance of wire will be R/4 (or 0.25 R).

The S.I. unit of electrical resistance is ohm (Ω). The resistance of a conductor is said to be 1 ohm if 1 ampere current flows through it when the potential difference across its end is 1 volt.

On stretching the wire to double its length, the length is doubled and its area of cross-section is reduced to half. So the resistance becomes four times i.e. the resistance of wire will become: 4 × 5Ω = 20 Ω.