Electric Circuit

An electric circuit is a setup that allows electric current to flow through connected components, making devices work, like lighting up a bulb.

Components of the Circuit:

1. Cell holder: This holds the dry cells (batteries) that provide the energy needed for the current.
2. Electric bulb: lights up when current flows through it.
3. Plug key: acts like a switch that can open or close the circuit.
4. Wires: Connect all the components, allowing the current to travel through them.

A circuit diagram is a graphical representation of an electrical circuit. A schematic diagram shows the components and interconnections of the circuit using standardised symbolic representations, while a pictorial circuit diagram uses simple images of components.

Components	Symbol
1. An electric cell
2. A battery or a combination of cells
3. Plug key or switch (open)
4. Plug key or switch (closed)
5. A wire joint
6. Wires crossing without joining
7. Electric bulb
8. A resistor of resistance R
9. Variable resistance or rheostat
10. Ammeter
11. Voltmeter

1. Closing the plug key completes the circuit after fitting the dry cell in the cell holder (Fig. a) and connecting the components as shown in Fig. b.
2. Once the plug key is closed, electric current flows from the cell through the wires to the bulb, making it light up.
3. The circuit breaks if you remove the cell or open the plug key. This stops the current, and the bulb goes off.

 (a) Cell holder

(b) Simple electric circuit

An electric circuit is a continuous path that allows electric current to flow. It consists of conducting wires, a cell (or battery), and other components like resistors, all connected in a loop. Electric circuits study or utilise the current flow, measure electrical quantities such as current and voltage, and regulate the operation of electrical devices. A circuit diagram shows the arrangement of components in a circuit. And it uses special symbols to represent components like resistors, batteries, wires, ammeters, and voltmeters.

Components in the Circuit:

• Electric Cell: Provides the potential difference required to drive current through the circuit.
• Ammeter: Connected in series with the circuit to measure the current flowing through it.
• Voltmeter: Connected in parallel with the resistor to measure the potential difference across it.

Electrical Circuit

1. Aim: To study the transfer of electrical energy in a circuit and verify Joule’s Law of Heating.

2. Requirements: Connecting wires, electric cells (battery), electrical resistor (R), voltmeter (V), ammeter (A), and plug key (switch).

3. Procedure

Set up the circuit as shown in the diagram, ensuring all components are properly connected.

Close the switch to allow current (I) to flow through the circuit.

Measure the current (I) using the ammeter.

Measure the potential difference (V_AB) across the resistor using the voltmeter.

Observe energy transfer:

• The potential at point A is higher than at point B, as A is connected to the positive terminal of the cell.
• As charge (Q) moves from A to B, electrical energy (V_AB × Q) is supplied by the battery to the resistor.
• The resistor converts electrical energy into heat, increasing its temperature.

Electric circuit

Key Equations:

Electrical Power: P = V_AB × I

Heat Produced (Joule’s Law of Heating): H = I² × R × t

4. Conclusion: The experiment shows that a resistor converts electrical energy into heat, following Joule’s Law of Heating. The amount of heat produced depends on the current, resistance, and time for which the current flows. The unit of electrical power is 1 watt (W), defined as 1 joule per second.

Joule’s law explains how electrical energy is converted into heat energy when an electric current flows through a resistor. The heat produced depends on the voltage, current, and resistance of the circuit.

Electrical Power and Heat Generation:

1. Definition of Electrical Power
Electrical power (P) is the rate at which electrical energy is supplied to a circuit. It is given by:

\[\mathrm{P=Electrical~power=\frac{Energy}{Timerequired}=\frac{V_{AB}Q}{t}=V_{AB}I}\] 

where V_AB is the potential difference across the resistor, I is the current, and Q is the charge.

2. Heat Produced in a Resistor
The energy supplied by the cell in time t is:

H = P × t = V_AB × I × t

By Ohm’s Law:

V_AB = I × R

Substituting this in the heat equation:

\[\mathrm{H}=\mathrm{V}_{\mathrm{AB}}^{2}\times\frac{\mathrm{t}}{\mathrm{R}}\]

or

H = I × I × R × t = I² × R × t

This equation is known as Joule’s Law of Heating, which states that the heat produced in a resistor is directly proportional to the square of the current, resistance, and time.

3. Unit of Electrical Power
Electrical power is also expressed as:

P = V_AB × I = Volt × Ampere

Since 1 Volt × 1 Ampere is equal to:

\[\begin{array}
{cc}1\text{Volt x 1 Amp}= & \frac{1\mathrm{J}}{1\mathrm{C}}\mathrm{x}\frac{1\mathrm{C}}{1\mathrm{s}}
\end{array}\]

\[\begin{array}
{rl}\frac{1\mathrm{J}}{1\mathrm{s}} & =\mathrm{W}\left(\mathrm{watt}\right)
\end{array}\]

The unit of electrical power is 1 Watt (W), which means 1 Joule of energy is consumed per second.