Ohm's Law – Long Answer Questions (CBSE Class 10 Science - Electricity)

Medium Level (Application & Explanation)

Answer:

Ohm’s Law states that the current through a conductor is directly proportional to the potential difference across it, if temperature remains constant.
Mathematically, $V = IR$ , where $V$ is voltage, $I$ is current, and $R$ is resistance.
For example, if a resistor has $R = 10\,\Omega$ and voltage applied is $5\,V$ , then current $I = 5/10 = 0.5\,A$ .
If the voltage is doubled to $10\,V$ , current also doubles to $1\,A$ .
This example shows that as voltage increases, current increases by the same factor, keeping resistance same.
Thus, Ohm’s Law provides a simple relationship to predict how current will change if we alter the voltage.

Answer:

Ohm’s Law is valid only when temperature and physical conditions remain unchanged.
Some devices, like the filament of an electric bulb, do not obey this law.
As more current passes, their temperature rises and resistance changes.
For example, an incandescent bulb’s resistance increases as it gets hotter, so current does not increase in direct proportion to voltage.
Devices like diodes and transistors also do not follow Ohm’s Law; their V-I graph is not a straight line.
Therefore, Ohm's Law is only for ohmic conductors (like metals at constant temperature), not non-ohmic devices.

Answer:

In a V-I graph for a metallic resistor, voltage (V) is on the y-axis and current (I) on the x-axis.
The graph is a straight line passing through the origin.
The slope of this line represents the resistance (R) of the resistor.
Mathematically, slope $= V/I = R$ .
A steeper line (more slope) means higher resistance—more voltage is needed for the same current.
Slope helps us easily compare different resistors by just looking at their V-I graphs.

Answer:

The water flow analogy makes the concept of electricity easier.
Voltage (V) is like the water pressure that pushes water through a pipe.
Current (I) is the flow of water itself—the actual movement of water drops.
Resistance (R) is like the narrowness of the pipe; a narrow pipe resists water flow, just like high resistance opposes electric current.
If pressure increases, more water flows (higher voltage means more current).
If the pipe gets narrower (resistance increases), less water flows for the same pressure (more resistance means less current for same voltage).
This analogy helps to visualize how V, I and R interact in a circuit.

Answer:

An ohmic conductor is a material or device that follows Ohm’s Law.
For these conductors, the current is directly proportional to the voltage, as long as temperature stays the same.
Examples include copper wire and a carbon resistor.
When you plot a V-I graph for these materials, you get a straight line passing through the origin.
This means constant resistance at all voltage and current values, under normal conditions.
Devices (like metals) with this property are widely used in electric circuits for predictable behavior.

Answer:

The bulb’s filament does not show direct proportionality between voltage and current.
As more current flows, the filament heats up; this causes the resistance to increase.
Resistance is not constant; it rises with increasing temperature due to rapid movement of atoms in the filament.
Thus, for each further increase in voltage, the increase in current is less than before.
The V-I graph becomes a curve, not a straight line, indicating a non-ohmic device.
This behavior proves Ohm’s Law does not apply whenever temperature changes in the conductor.

Answer:

According to Ohm’s Law, $V = IR$ or $I = V/R$ .
If resistance doubles, the denominator doubles.
With the same voltage, current will become half of its previous value.
For example, if $V = 10\,V$ and $R = 5\,\Omega$ , then $I = 2\,A$ .
If resistance increases to $10\,\Omega$ , $I = 1\,A$ .
This scenario shows the inverse relationship between resistance and current, highlighting how temperature changes affect electrical devices.

Answer:

For a metallic resistor, the V-I graph is a straight line through the origin.
This implies constant resistance and direct proportionality, following Ohm’s Law.
For a diode, the V-I graph is not straight; it is flat at first (almost no current), then curves upwards quickly after a certain voltage.
This shape means the diode only allows significant current in one direction, after crossing a threshold voltage.
The non-linear curve of the diode is due to its unique material and structure; it is a non-ohmic device.
Therefore, V-I graphs help in identifying which devices follow Ohm’s Law and which do not.

Answer:

The resistance of a wire is directly proportional to its length: $R \propto L$ .
If length is doubled, resistance becomes twice the original value.
Using Ohm’s Law ( $I = V/R$ ), if same voltage is applied, the current becomes half because resistance has doubled.
This shows why longer wires in circuits can reduce current flow.
In practical use, electrical wires are kept as short as possible to minimize resistance and loss of current.
This principle is very important in home wiring and electrical installations.

Answer:

When the charger works for a long time, current flows through its internal circuit and resistor components.
Due to electric current, the resistors get warm as energy is lost as heat (Joule heating).
With increased temperature, the resistance of the components may increase.
As resistance increases, for the same voltage, current may decrease slightly, which can slow charging over time.
This warming is a practical example of how resistance and temperature are linked and why device efficiency can drop as they heat up.
Thus, Ohm’s Law helps explain not just the normal flow, but also the effects of heating and efficiency in daily life gadgets.