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Electricity: Circuits and their Components - Circuit Diagrams

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A circuit diagram is a simplified graphical representation of an electrical circuit using standardized symbols for components such as cells, bulbs, switches, and wires.

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The long thin line in a cell symbol represents the positive terminal (++), while the short thick line represents the negative terminal (−-).

Symbol for an electric cell showing the positive and negative terminals.
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A battery is formed by connecting two or more cells in series, where the positive terminal of one cell is connected to the negative terminal of the next.

Symbol for a battery consisting of two cells connected in series.
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When the switch is in the 'ON' position, the circuit is closed, allowing current to flow from the positive terminal to the negative terminal.

A closed circuit diagram with a switch in the ON position and current flowing.
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An electric circuit is incomplete or 'open' when the switch is in the 'OFF' position, preventing the flow of electric current.

📐Formulae

Vtotal=V1+V2+V3+⋯+VnV_{total} = V_1 + V_2 + V_3 + \dots + V_n

I=QtI = \frac{Q}{t}

H∝I2H \propto I^2

💡Examples

Problem 1:

A student wants to make a battery using 44 cells, where each cell has a potential of 1.5V1.5\text{V}. Calculate the total voltage of the battery.

Solution:

Vtotal=1.5V+1.5V+1.5V+1.5V=6.0VV_{total} = 1.5\text{V} + 1.5\text{V} + 1.5\text{V} + 1.5\text{V} = 6.0\text{V}

Explanation:

In a battery, the total voltage is the sum of the voltages of the individual cells connected in series. To calculate this using vertical addition: 1.51.51.5+1.56.0\begin{array}{r} 1.5 \\ 1.5 \\ 1.5 \\ + 1.5 \\ \hline 6.0 \end{array}

Problem 2:

Identify the state of the bulb if the switch is in the 'OFF' position and the circuit is connected to a 3V3\text{V} battery.

Solution:

The bulb will not glow.

Explanation:

When the switch is in the 'OFF' position, the circuit is 'open'. An open circuit has a break in the path, which means the electric current cannot flow from the positive terminal to the negative terminal of the battery. Therefore, the bulb remains dark.

Problem 3:

If a current of 2A2\text{A} flows through a circuit for 1010 seconds, how much charge QQ has passed through the wire?

Solution:

Q=I×t=2A×10s=20CQ = I \times t = 2\text{A} \times 10\text{s} = 20\text{C}

Explanation:

Using the formula for current I=QtI = \frac{Q}{t}, we can rearrange it to find charge QQ. Here, I=2I = 2 and t=10t = 10.

Problem 4:

Draw a circuit diagram for a setup containing two bulbs connected in series, a closed switch, and a battery. If one bulb fuses, will the other bulb glow?

Circuit diagram with a battery, closed switch, and two bulbs in series.

Solution:

No, the other bulb will not glow. In a series circuit, if one component (like a bulb) breaks, the circuit becomes open and the flow of electricity stops for all components.

Explanation:

Current has only one path to follow. A fused bulb acts like an open switch, breaking the entire path.

Problem 5:

Observe the diagram. If the total voltage of the battery is 6V6V and it is made of equal cells of 1.5V1.5V each, how many cells are in the battery?

A series of four cells representing a $6V$ battery.

Solution:

Total Voltage=6VTotal\ Voltage = 6V Voltage per cell=1.5VVoltage\ per\ cell = 1.5V Number of cells=61.5=4Number\ of\ cells = \frac{6}{1.5} = 4 There are 44 cells in the battery.

Explanation:

A battery is a combination of cells. The total voltage is the sum of the voltages of individual cells connected in series.