CBSE Class 10 Science (Physics): Electricity – Factors Affecting Resistance

Long Answer Questions & Answers

Answer:

Resistance is directly proportional to the length of a conductor.
This means, if you double the length, the resistance also doubles.
For example, if a 1-meter copper wire has 2 ohms resistance, then a 2-meter wire of the same thickness and material will have 4 ohms.
This is because electrons face more obstacles as they travel through a longer path.
In electric circuits, longer wires can cause energy loss due to higher resistance.
That’s why house wiring uses as short lengths as possible for efficient energy use.

Answer:

Resistance is inversely proportional to the area of cross-section.
When the area increases, more electrons can flow side by side without bumping into each other.
Suppose you have two copper wires of the same length, but wire A is twice as thick as wire B.
Wire A will have half the resistance of wire B.
This is why thicker wires are used in places where strong currents are needed.
It helps to prevent the wire from getting heated and wasting energy.

Answer:

Resistance also depends on the material, which is measured by its resistivity (ρ).
Copper has low resistivity, so it allows electric current to pass very easily.
Iron, on the other hand, has higher resistivity and offers more opposition to current.
For the same length and area, an iron wire will have higher resistance compared to a copper wire.
This is why copper is often used for electrical wiring, while iron is not.
Choosing the right material is important for safety and efficiency.

Answer:

Resistivity (ρ) is a property specific to a material, showing how strongly it resists current.
It does not depend on the shape or size of the material, only its nature.
Resistance (R) depends on both resistivity and dimensions (length/area) of the material: $R = \rho \frac{L}{A}$ .
Resistivity is measured in ohm-meter (Ω·m), while resistance is in ohms (Ω).
For example, copper and iron wires of same size have different resistances due to their resistivity difference.
So, resistivity helps us compare materials, not objects.

Answer:

In most metallic conductors, resistance increases with temperature.
As temperature rises, atoms in the material vibrate more.
Electrons find it harder to move, so resistance goes up.
For example, the filament in a bulb gets very hot, so its resistance increases and it glows.
In contrast, some materials called semiconductors have resistance that decreases with temperature.
That is why temperature control is important in many electrical devices.

Answer:

To make an electric heater, you need a wire with high resistance so it gets hot easily.
First, choose a material with high resistivity, like nichrome.
Second, make the wire long and thin (increase length, reduce area) to raise resistance.
The wire should also withstand high temperatures without breaking.
By controlling these factors, the wire heats up quickly when current flows through it.
That’s why the selection and size of the wire are very important in heating appliances.

Answer:

The statement is incorrect.
If length is doubled, resistance doubles ( $R \propto L$ ).
If diameter is doubled, area becomes four times bigger ( $A \propto \text{diameter}^2$ ), so resistance becomes one-fourth ( $R \propto 1/A$ ).
So, total resistance = $2 \times (1/4) = 0.5$ times the original.
The resistance will become half, not stay the same.
This shows how both length and area affect resistance differently.

Answer:

Copper is preferred because it has a low resistivity and offers less resistance.
Thick wires have a large area, reducing resistance even further.
Lower resistance means less heat is produced and less energy is wasted as heat.
Iron has higher resistivity and thin wires cause more resistance, which can lead to overheating and possible fire risks.
Copper wires are also more durable and safe.
Therefore, thick copper wires provide both safety and efficiency.

Answer:

Long wires have more resistance, causing power loss as heat.
To minimize loss, use materials with low resistivity (like aluminum or copper).
Increase the area of cross-section (thicker wires) to reduce resistance.
Also, in practice, electric power is transmitted at high voltage and low current to reduce loss (as power loss is proportional to current squared).
Therefore, careful material choice and wire size are crucial in transmission lines.
This ensures electricity is delivered efficiently.

Answer:

Both wires are made of the same material and length, but have different areas.
The thinner wire (smaller area) will have higher resistance.
When the same current passes through both, the wire with higher resistance (thinner one) will produce more heat ( $H = I^2R$ ).
This is due to more collisions among electrons in the narrow path.
In practical use, this is the principle behind heating elements in appliances.
So, the thinner wire heats up more when current flows.