NCERT solutions for Class 10th Science Electricity

The energy given to each coulomb of charge passing through a 6 V battery is calculated using the formula:
Energy = Voltage × Charge

Here, the voltage is 6 V and the charge is 1 coulomb.
Energy = 6 V × 1 C = 6 Joules

So, the energy given to each coulomb of charge is 6 joules.

An electric circuit is a closed path through which electric current can flow. It usually includes a power source like a battery, wires to carry the current, and a device like a bulb or fan that uses the electricity.

If the path is complete (closed), electricity flows and the device works. If the path is broken (open), electricity cannot flow and the device does not work.

Unit of Current:The SI unit of electric current is the ampere (A).

Definition :-  One ampere is the current when one coulomb of charge flows through a conductor in one second.
So,  1 ampere = 1 coulomb / 1 second

To find the number of electrons in one coulomb of charge:

Charge of one electron = 1.6 × 10⁻¹⁹ coulombs
Number of electrons = 1 ÷ (1.6 × 10⁻¹⁹)
= 6.25 × 10¹⁸ electrons

Hence  6.25 × 10¹⁸ electrons make up one coulomb of charge.

Cell or Battery, These devices supply electrical energy and create the necessary potential difference to allow current to flow through a circuit.

When we say that the potential difference between two points is 1 volt (1 V), it means that 1 joule of work is done to move 1 coulomb of charge from one point to the other.

In simple words:
1 volt = 1 joule / 1 coulomb

The resistance of a conductor depends on the following factors:

1. Length of the conductor (L): Resistance increases with length.
   (More length → More resistance)
2. Area of cross-section (A): Resistance decreases with a larger area.
   (More thickness → Less resistance)
3. Material of the conductor:  Different materials have different resistivities.
   (Some materials oppose current more than others)
4. Temperature: Resistance increases with temperature (for most conductors).

Current will flow more easily through a thick wire than a thin wire of the same material when connected to the same source. 
Because a thick wire has a larger area of cross-section, so it offers less resistance to the flow of current. Lower resistance means more current can flow.

If the resistance of an electrical component remains constant and the potential difference across it decreases to half of its original value, then the current flowing through it will also change.

According to Ohm’s Law:
Current (I) = Potential difference (V) ÷ Resistance (R)

Since resistance (R) is constant, if the potential difference (V) becomes half, then the new current will be:
I new = (1/2 × V) ÷ R = (1/2) × (V ÷ R) = (1/2) × I original

This means the current will become half of its original value.

Coils of electric toasters and electric irons are made of an alloy rather than a pure metal due to following reasons:

1. Alloys have higher resistance than pure metals, so they produce more heat when electric current passes through them, which is useful for heating devices.
2. Alloys do not melt easily,  they have higher melting points, so the coils can withstand high temperatures without melting.
3. Alloys are more durable and strong,so the coils last longer under repeated heating and cooling.

Advantages of connecting electrical devices in parallel instead of in series:

1. Each device gets the full voltage of the battery:
   In parallel, every device gets the same voltage as the battery voltage, so all devices work properly.
2. Devices work independently:
   If one device stops working or is switched off, the others continue to work because they have their own separate paths.
3. Current is divided among devices:
   Total current is split according to resistance, preventing any one device from getting too much current.
4. Adding more devices does not reduce voltage:
   You can add more devices without reducing the voltage across each device.

The cord of an electric heater does not glow because it is made of a material with low resistance, so it does not heat up much.

The heating element glows because it is made of a material with high resistance, which causes it to get very hot and produce light when current passes through it.

Given:
Charge (Q) = 96000 coulombs
Potential difference (V) = 50 volts

Formula:
Heat generated (H) = Voltage (V) × Charge (Q)
H = 50 × 96000 = 4800000 joules

Hence the heat generated is 4800000 joules (4.8 million joules).

Given:
Resistance (R) = 20 ohms
Current (I) = 5 amperes
Time (t) = 30 seconds

Formula:
Heat developed (H) = I² × R × t
H = 5² × 20 × 30 = 25 × 20 × 30 = 15000 joules

Hence heat developed in 30 seconds = 15000 joules

The rate at which energy is delivered by a current is called power.

Power (P) = Voltage (V) × Current (I)

So, the rate of energy delivery depends on both the voltage and the current.