• Recall and use standard circuit symbols (e.g., for cells, batteries, switches, lamps, resistors (fixed and variable), voltmeters, ammeters, diodes, LDRs, thermistors, capacitors, LEDs).
• Draw and interpret circuit diagrams containing these symbols.
• Understand the function of common components in simple circuits.
• Distinguish between series and parallel connections in circuit diagrams.

• Define and use key vocabulary related to electric circuits and their components (e.g., cell, battery, switch, resistor, ammeter, voltmeter, series, parallel).
• Describe the purpose of different circuit components using appropriate scientific language.
• Explain how to draw a circuit diagram from a description.
• Verbally interpret a given circuit diagram.

Here are some important terms for this lesson. Pay attention to their meanings and translations.

Review the key terms and circuit symbols using flashcards. You can create your own set on Quizlet or use a pre-existing one focusing on A-Level Physics circuit symbols.

(Instructor: Embed Quizlet flashcards here. Example: )

Placeholder for Quizlet embed code. Please replace this with your actual Quizlet set or search for one like «A-Level Physics Circuit Symbols».

Circuit Diagram: A graphical representation of an electrical circuit using standard symbols for components and lines for connecting wires.

Cell: A device that converts chemical energy into electrical energy, providing a potential difference (voltage). Symbol: Long line (positive terminal) and short line (negative terminal).

Battery: A combination of two or more cells connected together, usually in series, to provide a larger voltage. Symbol: Multiple cell symbols connected.

Ammeter: An instrument used to measure electric current in a circuit. It is always connected in series with the component whose current is being measured. Symbol: A circle with ‘A’ inside.

Voltmeter: An instrument used to measure potential difference (voltage) across a component or part of a circuit. It is always connected in parallel with the component. Symbol: A circle with ‘V’ inside.

Understanding electrical circuitsэлектр тізбектері / электрические цепи is fundamental in physics and engineering. A circuit diagramтізбек сызбасы / схема цепи is a simplified, standardized way to represent a circuit using specific symbols for each component.

Common Circuit Symbols:

It is crucial to memorize these symbols as they form the language of electronics. Here are some of the most common ones you’ll encounter in AS/A Level Physics:

• Cell: Provides the electromotive force (e.m.f.)электр қозғаушы күш (ЭҚК) / электродвижущая сила (ЭДС) to drive current. The longer line is the positive (+) terminal, and the shorter line is the negative (-) terminal. Current conventionally flows from positive to negative.
  
  [Image of Cell Symbol]
• Battery: A series of cells. The total e.m.f. is the sum of individual cell e.m.f.s (if connected in the same direction).
  
  [Image of Battery Symbol]
• Switch (Open): Breaks the circuit, stopping current flow.
  
  [Image of Open Switch Symbol]
• Switch (Closed): Completes the circuit, allowing current to flow.
  
  [Image of Closed Switch Symbol]
• Lamp (Bulb): Converts electrical energy to light and heat.
  
  [Image of Lamp Symbol]
• Fixed Resistor: Opposes the flow of current. Has a constant resistanceкедергі / сопротивление.
  
  [Image of Fixed Resistor Symbol]
• Variable Resistor (Rheostat): Allows the resistance in the circuit to be changed.
  
  [Image of Variable Resistor Symbol]
• Voltmeter: Measures potential difference (voltage)потенциалдар айырымы (кернеу) / разность потенциалов (напряжение) across a component. Connected in parallelпараллель / параллельно. Ideally has infinite resistance.
  
  [Image of Voltmeter Symbol]
• Ammeter: Measures currentток күші / сила тока flowing through a component. Connected in seriesтізбектей / последовательно. Ideally has zero resistance.
  
  [Image of Ammeter Symbol]
• Diode: Allows current to flow in one direction only (forward bias).
  
  [Image of Diode Symbol]
• Light Emitting Diode (LED): A diode that emits light when current flows through it in the forward direction.
  
  [Image of LED Symbol]

(Source: Adapted from Cambridge AS/A Level Physics syllabus and common textbook representations like SaveMyExams)

Drawing Circuit Diagrams:

1. Use straight lines for wires.
2. Wires should connect at junctions, often shown with a dot, or cross without connecting if no dot is present (though clear separation is better).
3. Arrange symbols clearly, without overcrowding.
4. Ensure the circuit is complete (forms a closed loop) for current to flow, unless a switch is intentionally open.
5. Place ammeters in series with the component whose current you want to measure.
6. Place voltmeters in parallel across the component whose potential difference you want to measure.

Interpreting Circuit Diagrams:

When you look at a circuit diagram, you should be able to:

• Identify each component by its symbol.
• Understand the function of each component.
• Trace the path of conventional current (from + to -).
• Determine if components are connected in series (one after another, forming a single path for current) or in parallel (connected across the same two points, providing multiple paths for current).

Questions on Theory:

1. (Easy) Draw the circuit symbol for a battery consisting of three cells.
   
   Answer

   The symbol should show three cell symbols connected in series: (+ -)(+ -)(+ -) or |i|i|i (using simplified text).
   
   [Image of 3-Cell Battery Symbol]
   
2. (Medium) Describe how an ammeter should be connected in a circuit to measure the current through a lamp, and explain why. What is the ideal resistance of an ammeter?
   
   Answer

   An ammeter should be connected in series with the lamp. This is because current is the rate of flow of charge, and to measure the current passing *through* the lamp, all the charge flowing through the lamp must also flow through the ammeter. The ideal resistance of an ammeter is zero, so it does not add any significant resistance to the circuit and alter the current it is trying to measure.
3. (Medium) A student wants to measure the potential difference across a resistor in a circuit. Draw a simple circuit diagram showing a cell, a switch, the resistor, and a correctly placed voltmeter to measure the p.d. across the resistor.
   
   Answer

   The circuit diagram should show:

   • A cell symbol.
   • A switch symbol (can be open or closed) in series with the cell and resistor.
   • A resistor symbol.
   • A voltmeter symbol connected in parallel *across* the resistor (i.e., its terminals connect to either side of the resistor).

   [Image of Circuit with Cell, Switch, Resistor, and Voltmeter across Resistor]
   

4. (Hard — Critical Thinking) Consider a circuit with one cell, a switch, and two lamps. How would you connect the lamps so that if one lamp breaks (the filament snaps, creating an open circuit within that lamp), the other lamp continues to light up? Draw the circuit diagram and explain your reasoning.
   
   Answer

   The lamps should be connected in parallel.
   
   [Image of Circuit with Cell, Switch, and Two Lamps in Parallel]
   
   Reasoning: In a parallel circuit, each lamp has its own separate path (branch) for the current to flow from the cell. If one lamp breaks, its path becomes an open circuit, and current stops flowing through that branch. However, the other lamp is on a different, independent path, which remains a closed circuit. Therefore, current can still flow through the second lamp, and it will continue to light up. If they were in series, a break in one lamp would break the entire single path for current, and both lamps would go out.
   

Exercise 1: Match the Component with its Symbol’s Description

1. Cell
2. Voltmeter
3. Fixed Resistor
4. Open Switch
5. LED

A. A rectangle.
B. A circle with ‘V’ inside.
C. A break in the line with two small circles at the ends of the break.
D. A long line and a parallel short line.
E. A diode symbol with two small arrows pointing away from it.

Exercise 2: Fill in the Blanks

1. A __________ is used to measure the current flowing in a circuit and is connected in __________.
2. To provide a variable resistance in a circuit, you would use a __________.
3. A battery is a collection of __________ connected together.
4. A __________ allows current to flow in only one direction.
5. The circuit symbol for a lamp is a circle with a __________ inside it.

Watch this video to learn about common circuit symbols and how to draw circuit diagrams:

(Please verify the suitability of this video or replace it with one specifically for A-Level if preferred.)

Additional Recommended Videos:

Problem 1: Draw a circuit diagram to show a battery of two cells connected in series to a switch, which is then connected to two lamps in parallel. Include an ammeter to measure the total current from the battery and a voltmeter to measure the potential difference across one of the lamps.

Problem 2: Interpret the following circuit diagram. Identify all components and describe how they are connected (series/parallel). What does the ammeter measure? What does the voltmeter measure?

[Image of a sample circuit diagram for Problem 2, e.g., a cell, a switch, a fixed resistor R1, then a parallel branch with R2 and a lamp, and an ammeter before R1, and a voltmeter across R2.]

Explore basic circuits using the PhET Interactive Simulation «Circuit Construction Kit: DC».

Simulation Link: Circuit Construction Kit: DC

Instructions & Questions:

1. Open the simulation. Familiarize yourself with dragging components (battery, wires, lamp, resistor, switch) from the toolbox and connecting them.
2. Task 1 (Simple Circuit): Construct a simple circuit with one battery (e.g., 9V), one switch, and one lamp (e.g., 10Ω resistance). Close the switch.
   
   Question 1a: Does the lamp light up? What happens if you open the switch?
   
   Answer Q1a

   Yes, the lamp lights up when the switch is closed, completing the circuit. If the switch is opened, the circuit is broken, current stops flowing, and the lamp goes out.
   
   Question 1b: Use the «Voltmeter» and «Ammeter» tools from the right panel. Measure the current flowing from the battery and the voltage across the lamp. Record these values.
   
   Answer Q1b

   To measure current, break the circuit and insert the ammeter in series. To measure voltage, place the voltmeter probes across the lamp. (Values will depend on the specific battery voltage and lamp resistance chosen, e.g., for 9V battery and 10Ω lamp, current I = V/R = 9/10 = 0.9A. Voltage across lamp will be close to 9V if it’s the only component).
3. Task 2 (Series Circuit): Add a second identical lamp in series with the first lamp.
   
   Question 2a: What do you observe about the brightness of the lamps compared to when there was only one lamp?
   
   Answer Q2a

   The lamps will be dimmer than when there was only one lamp. This is because the total resistance of the circuit has increased, so the current from the battery decreases. Also, the battery voltage is now shared between the two lamps.
   
   Question 2b: Measure the current in the circuit and the voltage across each lamp. How does the sum of voltages across the two lamps compare to the battery voltage?
   
   Answer Q2b

   The current will be the same through both lamps and will be less than in Q1b. The sum of the voltages across the two lamps should be approximately equal to the battery voltage (Kirchhoff’s Voltage Law).
4. Task 3 (Parallel Circuit): Now, connect the two identical lamps in parallel with each other, powered by the same battery and switch.
   
   Question 3a: What do you observe about the brightness of the lamps compared to the series circuit (Task 2) and the single lamp circuit (Task 1)?
   
   Answer Q3a

   The lamps in parallel will be brighter than when they were in series and should be about as bright as the single lamp in Task 1 (assuming the battery can supply the increased total current).
   
   Question 3b: Measure the voltage across each lamp and the current through each lamp. Also, measure the total current leaving the battery. How does the total current compare to the current in each branch?
   
   Answer Q3b

   The voltage across each lamp in parallel will be approximately equal to the battery voltage. The total current leaving the battery will be the sum of the currents flowing through each parallel branch (Kirchhoff’s Current Law).

Work with a partner or in a small group.

Activity: «Circuit Diagram Challenge»

1. One person describes a simple circuit verbally (e.g., «A battery connected to a switch, then to a resistor and a lamp in series. A voltmeter is connected across the resistor.»).
2. The other person (or group members) tries to draw the circuit diagram accurately using correct symbols.
3. Compare the drawing with the description and discuss any discrepancies.
4. Take turns describing and drawing. Try circuits with both series and parallel components.

(Alternatively, use an online tool like Quizizz or LearningApps.org for a collaborative quiz on identifying circuit symbols or interpreting simple diagrams. Instructor: Please search for «circuit symbols quiz» or «simple circuits quiz» on these platforms.)

Placeholder for embedded activity if using an online tool.

Answer the following questions. Show your working and draw circuit diagrams where necessary.

1. Draw a circuit diagram showing a 12V battery connected to a switch. When the switch is closed, the current flows through a fixed resistor of 100Ω. An LED is also connected in the circuit in series with a protective resistor R_P, such that the LED and its protective resistor are in parallel with the 100Ω resistor.
   
   (a) Draw this circuit diagram.
   
   (b) If the LED requires a current of 20mA and has a forward voltage of 2V, and it is to be powered from the 12V supply, what is the purpose of R_P?
   
   (c) Explain why directly connecting the LED to the 12V supply without R_P would likely damage it.
   
   Answer 1

   (a) [Image of the circuit diagram: 12V battery, switch in main line. Then a 100Ω resistor. In parallel to this 100Ω resistor, a branch containing an LED symbol and a resistor symbol (R_P) in series.]
   
   Diagram description: A 12V battery symbol is connected in series with a switch symbol. After the switch, the circuit splits into two parallel branches. Branch 1 contains a 100Ω resistor. Branch 2 contains an LED symbol in series with another resistor symbol labelled R_P. Both branches then rejoin and connect back to the battery.

   (b) The purpose of the protective resistor R_P is to limit the current flowing through the LED to its safe operating value (20mA in this case) and to drop the excess voltage from the 12V supply so that the voltage across the LED is its required forward voltage (2V).

   (c) LEDs have a very low internal resistance when forward biased. If connected directly to a 12V supply without R_P, a very large current would flow through the LED (I = V/R, with R being very small). This large current would cause excessive heating and would likely burn out and damage the LED almost instantly. R_P provides the necessary resistance to keep the current at a safe level.
   

2. A student sets up a circuit with a variable power supply, an ammeter, a voltmeter, and an unknown component ‘X’. The ammeter is in series with ‘X’ and the power supply. The voltmeter is in parallel with ‘X’.
   The student varies the voltage from the power supply and records the corresponding current. The results are:
   Voltage (V): 0, 1.0, 2.0, 3.0, 4.0, 5.0
   Current (A): 0, 0.05, 0.10, 0.15, 0.20, 0.25
   
   (a) Draw the circuit diagram the student would have used.
   
   (b) Plot a graph of Voltage (on y-axis) against Current (on x-axis).
   
   (c) What can you deduce about component ‘X’ from the graph? Calculate its resistance if appropriate.
   
   Answer 2

   (a) [Image of circuit: Variable power supply symbol, ammeter symbol in series, component ‘X’ (represented by a box), all in a loop. Voltmeter symbol connected in parallel across component ‘X’.]
   
   Diagram description: A variable DC power supply symbol is connected in series with an ammeter symbol, which is then connected in series with a box labelled ‘X’ (representing the unknown component). This completes the series loop back to the power supply. A voltmeter symbol is connected with its terminals on either side of component ‘X’.

   (b) The graph of V against I should be a straight line passing through the origin.
   
   [Description of graph: Y-axis labelled «Voltage (V)», X-axis labelled «Current (A)». Points plotted: (0,0), (0.05,1.0), (0.10,2.0), (0.15,3.0), (0.20,4.0), (0.25,5.0). A straight line of best fit drawn through these points.]

   (c) Since the graph of V against I is a straight line through the origin, component ‘X’ is an ohmic conductor (it obeys Ohm’s Law). Its resistance is constant.
   
   The resistance R = V/I = slope of the V-I graph.
   
   Using the point (5.0V, 0.25A): R = 5.0V / 0.25A = 20Ω.
   
   (The slope can be calculated more formally: e.g., (5-0)/(0.25-0) = 20Ω).
   

3. Compare and contrast connecting two identical lamps in series versus connecting them in parallel to the same battery. Discuss:
   
   (a) The brightness of the lamps in each configuration.
   
   (b) What happens if one lamp breaks in each configuration.
   
   (c) The total resistance of the lamp combination in each case compared to a single lamp.
   
   Answer 3

   (a) Brightness:
   
   Series: The lamps will be dimmer than a single lamp connected to the same battery. They share the battery voltage, and the total resistance is higher, leading to lower current. Both lamps will have the same brightness (if identical).
   
   Parallel: The lamps will be brighter than in the series configuration, and each will be approximately as bright as a single lamp connected to the same battery (assuming the battery can supply the necessary current). Both lamps have the full battery voltage across them.

   (b) If one lamp breaks:
   
   Series: If one lamp breaks, the circuit becomes open, and current stops flowing. The other lamp will also go out.
   
   Parallel: If one lamp breaks, it only opens its own branch of the circuit. The other lamp, being in a separate parallel branch, will continue to operate normally.

   (c) Total Resistance (R_lamp is resistance of one lamp):
   
   Series: Total resistance R_total = R_lamp + R_lamp = 2R_lamp. This is higher than a single lamp.
   
   Parallel: Total resistance 1/R_total = 1/R_lamp + 1/R_lamp = 2/R_lamp. So, R_total = R_lamp/2. This is lower than a single lamp.
   

4. Draw a circuit diagram that includes: a battery, a switch, a thermistor, and a fixed resistor connected in series. A voltmeter is connected to measure the potential difference across the fixed resistor. Explain how the reading on the voltmeter would change if the temperature of the thermistor increases. (Assume it is an NTC thermistor, whose resistance decreases with increasing temperature).
   
   Answer 4

   [Image of circuit: Battery, switch, thermistor symbol, fixed resistor symbol all in series. Voltmeter symbol connected in parallel across the fixed resistor.]
   
   Diagram description: A battery symbol, switch symbol, thermistor symbol (resistor with a diagonal line through it and a hockey-stick like line indicating temperature dependence), and a fixed resistor symbol are all connected in a single series loop. A voltmeter symbol is connected with its terminals on either side of the fixed resistor.

   Explanation:
   
   1. An NTC (Negative Temperature Coefficient) thermistor’s resistance decreases as its temperature increases.
   
   2. The thermistor and the fixed resistor are in series, forming a potential divider. The total resistance of the circuit is R_total = R_thermistor + R_fixed.
   
   3. If the temperature of the thermistor increases, R_thermistor decreases.
   
   4. This causes the total circuit resistance (R_total) to decrease.
   
   5. According to Ohm’s Law (I = V_battery / R_total), if R_total decreases and V_battery is constant, the total current (I) flowing in the series circuit increases.
   
   6. The voltmeter measures the potential difference across the fixed resistor (V_fixed = I * R_fixed).
   
   7. Since R_fixed is constant and the current I increases, the potential difference V_fixed across the fixed resistor will increase.
   
   Therefore, the reading on the voltmeter would increase if the temperature of the NTC thermistor increases.
   

5. Design and draw a circuit diagram for a system where a Light Dependent Resistor (LDR) is used to automatically switch on an LED when it gets dark. Your circuit should include a power source, the LDR, the LED, and any necessary resistors. Explain briefly how your circuit works. (Hint: You might need to think about a potential divider and how another component like a transistor could be used as a switch, but for A-Level, a conceptual explanation with a potential divider influencing the LED directly or via a simple comparator idea is often sufficient if transistors are not yet covered).
   
   Answer 5

   (This is a more advanced design question. A simple version uses a potential divider.)
   
   Circuit Diagram (Simple Potential Divider Version):
   
   [Image of circuit: A battery. A series combination of an LDR and a fixed resistor (R1), forming a potential divider. The LED, with its own series protective resistor (R_LED), is connected in parallel across the fixed resistor R1.]
   
   Diagram description: A battery is connected to a series circuit consisting of an LDR symbol and a fixed resistor symbol (R1). This forms a potential divider. The junction point between the LDR and R1 is one connection point for a parallel branch. The other connection point for this parallel branch is the other side of R1 (or the negative terminal of the battery if R1 is connected to it). Across these two points (i.e., in parallel with R1), an LED symbol is connected in series with its own protective resistor (R_LED).

   Explanation:
   
   1. The LDR and the fixed resistor R1 form a potential divider. The voltage across R1 (V_R1) depends on the resistance of the LDR.
   
   2. The resistance of an LDR is high in the dark and low in bright light.
   
   3. In bright light: The LDR has low resistance. According to the potential divider formula (V_R1 = V_supply * (R1 / (R_LDR + R1))), if R_LDR is low, the voltage V_R1 across R1 will be relatively high (if R1 is significantly larger than R_{LDR_light}). Correction: For the LED to be OFF in light, we want V_R1 to be LOW in light. So, the LED should be across the LDR, or R1 should be chosen carefully. Let’s re-think the connection for «ON in dark».

   Revised Circuit Diagram & Explanation for «ON in Dark»:
   
   [Image of revised circuit: A battery. A series combination of a fixed resistor (R1) and an LDR, forming a potential divider. The LED (with its series protective resistor R_LED) is connected in parallel across the LDR.]
   
   Diagram description (Revised): A battery is connected to a series circuit consisting of a fixed resistor symbol (R1) and an LDR symbol. This forms a potential divider. The LED (with R_LED) is connected in parallel across the LDR.

   Revised Explanation:
   
   1. The fixed resistor R1 and the LDR form a potential divider. The voltage across the LDR (V_LDR) is what the LED (and its resistor) will experience.
   
   2. In bright light: The LDR has low resistance. The voltage across the LDR (V_LDR = V_supply * (R_LDR / (R1 + R_LDR))) will be low. If this voltage is below the forward voltage required for the LED to light up, the LED will be OFF.
   
   3. In the dark: The LDR’s resistance becomes very high. Now, V_LDR will be high (a larger fraction of V_supply). If this voltage is sufficient, current will flow through the LED (and R_LED), and the LED will switch ON.
   
   4. R_LED is a current-limiting resistor for the LED, chosen to protect it when V_LDR is high. R1 is chosen to ensure the voltage division works correctly for the desired light levels.
   
   (Note: For a more robust switching action, a transistor would typically be used, where the voltage from the potential divider controls the transistor’s base, and the transistor then switches a larger current for the LED.)
   

• Save My Exams — Circuit Symbols & Diagrams: (Search on Save My Exams for «A-Level Physics Circuit Symbols» or «DC Circuits») Save My Exams (A-Level Physics)
• PhysicsAndMathsTutor — Electricity: (Browse the Electricity section for notes on DC circuits and past papers) PhysicsAndMathsTutor (Example for OCR A, find your board)
• HyperPhysics — Electric Circuits: HyperPhysics Concepts
• ElectronicsTutorials.ws — Circuit Symbols: Electronics Tutorials — Circuit Symbols
• YouTube — The Organic Chemistry Tutor — Series and Parallel Circuits: Series and Parallel Circuits Explained

Take a few moments to reflect on your learning:

• Which circuit symbols are you most confident in recognizing and drawing? Which ones are still tricky?
• What is the key difference in connecting an ammeter versus a voltmeter in a circuit? Why is this important?
• Can you describe a real-world device and imagine what its basic circuit diagram might look like (e.g., a simple flashlight)?
• What was the most challenging question or concept in this lesson for you?
• How will you practice drawing and interpreting circuit diagrams further?