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Electricity - Series circuits and circuit diagrams

Grade 5Cambridge (IGCSE)

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

🔑Concepts

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A series circuit is a single continuous loop where all components are connected one after another. In this arrangement, there is only one path for the electric current to flow.

A circuit diagram showing a battery connected in a single loop to two lamps in series.
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Current (II) is the same at every point in a series circuit. If you measure the current near the battery or between two bulbs, the value remains constant: Itotal=I1=I2I_{total} = I_1 = I_2.

Circuit with two ammeters placed at different points showing that current is the same throughout.
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The total voltage (VV) provided by the power source is shared between the components. For example, if two identical bulbs are connected to a 3 V3\ V battery, each bulb receives 1.5 V1.5\ V.

Diagram illustrating voltage sharing in a series circuit.
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If any component in a series circuit breaks or is disconnected, the circuit becomes 'open'. This stops the flow of electricity entirely, and all other components will stop working.

📐Formulae

Itotal=I1=I2=I3I_{total} = I_1 = I_2 = I_3

Vtotal=V1+V2+V3V_{total} = V_1 + V_2 + V_3

Vbattery=Vcell1+Vcell2V_{battery} = V_{cell1} + V_{cell2}

💡Examples

Problem 1:

A series circuit contains two 1.5 V1.5\ V cells and one bulb. What is the total voltage VtotalV_{total} supplied to the bulb?

Solution:

Vtotal=1.5 V+1.5 V=3.0 VV_{total} = 1.5\ V + 1.5\ V = 3.0\ V

Explanation:

In a series circuit, the voltages of the cells are added together to find the total voltage supplied to the components.

Problem 2:

An ammeter placed next to the battery in a series circuit reads 0.2 A0.2\ A. What would another ammeter read if it was placed between two bulbs further down the same circuit?

Solution:

I=0.2 AI = 0.2\ A

Explanation:

In a series circuit, the current II is the same at all points because there is only one path for the electricity to follow.

Problem 3:

If a series circuit has three bulbs and one bulb 'blows' (the filament breaks), what happens to the other two bulbs?

Solution:

The other two bulbs will turn off.

Explanation:

A 'blown' bulb creates a gap in the circuit. Since there is only one path in a series circuit, the break stops the flow of current II entirely.

Problem 4:

A series circuit consists of a 9 V9\ V battery and two identical resistors, R1R_1 and R2R_2. If a voltmeter connected across R1R_1 measures 4.5 V4.5\ V, what is the voltage across R2R_2?

Circuit diagram with a 9V battery and two resistors in series.

Solution:

VR2=Vtotal−VR1V_{R2} = V_{total} - V_{R1} VR2=9 V−4.5 VV_{R2} = 9\ V - 4.5\ V VR2=4.5 VV_{R2} = 4.5\ V

Explanation:

In a series circuit, the sum of the voltages across individual components must equal the total voltage supplied by the battery. Since the resistors are identical, they share the voltage equally.

Problem 5:

A series circuit is constructed using a 12 V12\ V battery and three identical lamps, L1L_1, L2L_2, and L3L_3. If an ammeter placed after the battery reads 0.6 A0.6\ A, determine the current flowing through L2L_2 and the voltage drop across L3L_3.

Circuit diagram showing a 12V battery, an ammeter, and three lamps L1, L2, and L3 connected in a single series loop.

Solution:

  1. Current in a series circuit: Itotal=I1=I2=I3=0.6 AI_{total} = I_1 = I_2 = I_3 = 0.6\ A
  2. Voltage in a series circuit with identical components: Vtotal=V1+V2+V3V_{total} = V_1 + V_2 + V_3 Since the lamps are identical, V1=V2=V3=12 V3=4 VV_1 = V_2 = V_3 = \frac{12\ V}{3} = 4\ V

Explanation:

In a series circuit, there is only one path for the electrons to flow, so the current (II) remains the same at all points. Therefore, the ammeter reading of 0.6 A0.6\ A applies to every component. The total voltage supplied by the battery is shared equally among identical components connected in series. Dividing the total voltage (12 V12\ V) by the number of lamps (3) gives the voltage for each.