Electricity: Circuits and Their Components – Case-based Questions with Answers
CBSE Board Examinations – Case-Based Questions with Answers
This page provides a comprehensive, topic-wise set of 20 Case-Based Questions with clear answers for Class 7 Science – Chapter 3: Electricity: Circuits and Their Components. All questions are prepared strictly as per the NCERT syllabus and are ideal for:
- CBSE Class 7 board exam standard and school examinations
- Case-based and competency-based question practice
- Conceptual understanding of electric circuits and safety
Each case begins with a short real-life situation or data-based passage, followed by simple questions. Answers are given just below every case in student-friendly language for quick learning and revision.
Topic 1: Simple Circuits & Bulb Glowing
Case 1 – Riya’s Torch:
Riya wants to use her torch during a power cut. She inserts two new cells in the torch, closes the lid and presses the switch. However, the torch does not glow. She opens it again and checks the cells and bulb carefully. She realises that both cells are placed in the wrong direction.
- (a) What type of source of electricity is used in the torch?
- (b) In which direction should the cells be arranged in the torch?
- (c) Why did the bulb not glow when the cells were placed in the wrong direction?
- (d) After correcting the cells, what condition must be fulfilled for the bulb to glow?
Answers:
(a) The torch uses a battery, which is a combination of two or more electric cells.
(b) The positive terminal of one cell should touch the negative terminal of the next cell in a row.
(c) In the wrong direction, the terminals may not form a proper battery and the circuit may not get a correct potential difference, so current cannot flow.
(d) The cells must be placed correctly and the circuit must be closed (switch ON, no loose connection) for the bulb to glow.
Case 2 – Bulb on a Cardboard:
A teacher asks students to fix a bulb and a dry cell on a piece of cardboard using tape. The students use pieces of wire to connect the cell and bulb. In one group’s model, the bulb glows brightly. In another group’s model, the bulb does not glow at all.
- (a) Name the path along which electric current flows in this activity.
- (b) Mention any two possible reasons why the bulb is not glowing in the second group’s model.
- (c) How can students check if the bulb used by the second group is fused or not?
- (d) What will happen if the cell is removed from the glowing circuit?
Answers:
(a) The path is called an electric circuit.
(b) Possible reasons: (i) Loose or wrong connections causing an open circuit. (ii) The bulb may be fused or the cell may be weak/dead.
(c) They can connect the bulb in a known working circuit with a fresh cell; if it still does not glow, the bulb is fused.
(d) If the cell is removed, there will be no source of electrical energy and the bulb will stop glowing immediately.
Case 3 – Open or Closed?
Aditya makes a circuit using a cell, a bulb and a switch. He notices that when the switch is in position A, the bulb glows. When he flips the switch to position B, the bulb stops glowing. He wonders what is happening inside the circuit.
- (a) What is the function of a switch in a circuit?
- (b) In which position (A or B) is the circuit closed?
- (c) What happens to the path of current when the bulb is glowing?
- (d) Why does the bulb stop glowing when the switch is turned to position B?
Answers:
(a) A switch is used to open or close the circuit and control the flow of current.
(b) The circuit is closed in position A, when the bulb glows.
(c) The path of current is complete from one terminal of the cell, through the switch and bulb, back to the other terminal.
(d) In position B, the switch opens the circuit, creating a gap so current cannot flow and the bulb does not glow.
Topic 2: Electric Cell & Battery
Case 4 – Remote Control Cells:
A TV remote is not working properly. Meera opens the cover and finds two old cells inside. She replaces them with two fresh cells, keeping the positive terminal of one touching the negative terminal of the other. After closing the cover, the remote works again.
- (a) What type of cells are commonly used in TV remotes?
- (b) How many terminals does each cell have? Name them.
- (c) Why did the remote start working after replacing the cells?
- (d) What energy change takes place inside a cell when the remote is used?
Answers:
(a) Dry cells (small cylindrical cells) are commonly used.
(b) Each cell has two terminals: a positive terminal and a negative terminal.
(c) The old cells were discharged and could not provide enough energy. Fresh cells supply proper electrical energy to operate the remote.
(d) Chemical energy stored in the cell changes into electrical energy when the remote is used.
Case 5 – Weak Cell in a Toy Car:
A battery-operated toy car moves fast when new cells are used. After a few days the same car starts moving very slowly and finally stops, even though the switch is ON and connections are correct.
- (a) What is the most likely reason for the toy car slowing down?
- (b) What do we call a cell that can no longer provide enough energy?
- (c) How can we make the toy car work again?
- (d) Why should used/discharged cells not be thrown anywhere in the environment?
Answers:
(a) The cells in the toy car have become weak or discharged.
(b) It is called a dead cell or discharged cell.
(c) By replacing the weak cells with fresh cells or recharging them (if they are rechargeable cells).
(d) Cells contain chemicals which can pollute soil and water if thrown carelessly; they should be disposed of properly or recycled.
Case 6 – Short Circuit with a Cell:
Rahul connects the two terminals of a cell directly with a copper wire, without using any bulb or device. After some time, the cell becomes hot and weak. His teacher explains that this is not a safe way to connect a cell.
- (a) What is the mistake in Rahul’s connection?
- (b) What do we call this type of wrong connection?
- (c) Why did the cell become hot?
- (d) How should a cell normally be connected in a circuit?
Answers:
(a) He directly joined the positive and negative terminals of the cell with only a wire.
(b) This type of connection is called a short circuit.
(c) In a short circuit, a very large current flows through the wire with almost no resistance, which heats the cell and wire.
(d) A cell should be connected through some electrical device, like a bulb or resistor, so that current flows safely through the circuit.
Topic 3: Bulb, Filament & Fused Bulb
Case 7 – Street Light Not Working:
One evening, Rohan observes that all the street lights on his road are glowing except one. The electric poles and wires look fine. He guesses that only the bulb in that particular street light is faulty.
- (a) What do we call a bulb whose filament is broken?
- (b) Why does a bulb with a broken filament not glow?
- (c) If the rest of the circuit is fine, what needs to be done to repair the street light?
- (d) Which part of the bulb actually glows when current passes through it?
Answers:
(a) It is called a fused bulb.
(b) When the filament breaks, the path of current inside the bulb becomes open and current cannot pass through it.
(c) The faulty bulb needs to be replaced with a new working bulb.
(d) The thin wire inside the bulb, called the filament, glows when current flows through it.
Case 8 – Bulb Gets Hot:
In a school lab, students notice that a small electric bulb becomes hot after it glows for some time. The teacher tells them that electric current can produce heat and this helps the bulb to glow.
- (a) What effect of electric current is observed in a glowing bulb?
- (b) Why does the glass of the bulb become hot?
- (c) What precaution should be taken while handling a bulb that was glowing just a few moments ago?
- (d) Name any one other appliance that works on the heating effect of electric current.
Answers:
(a) The heating effect of electric current is observed.
(b) The filament inside gets very hot due to current and transfers heat to the glass, making it hot.
(c) We should switch off the supply and wait for the bulb to cool before touching or changing it.
(d) Electric iron, electric heater, electric kettle, geyser (any one).
Case 9 – Fault-Finding in a Circuit:
A simple circuit is made with a cell, a bulb and a switch. The bulb does not glow. The teacher suggests checking one component at a time by replacing it with a known working component.
- (a) Which components should be checked one by one to find the fault?
- (b) If replacing the bulb makes the new bulb glow, which part was faulty?
- (c) If the bulb still does not glow after changing it, which components should be checked next?
- (d) Why is it useful to replace one component at a time during fault finding?
Answers:
(a) The bulb, the cell and the switch/wires should be checked.
(b) The original bulb was faulty (possibly fused).
(c) The cell may be weak or the connections/wires or switch may be faulty and should be checked.
(d) Replacing one component at a time helps us identify exactly which component is causing the problem.
Topic 4: Conductors, Insulators & Water as Conductor
Case 10 – Testing Materials:
In the lab, students make a simple tester with a cell and a small bulb. They place different materials like copper wire, plastic scale, aluminium foil and rubber piece between the two free ends of the tester. The bulb glows with some materials but not with others.
- (a) For which type of materials will the bulb glow?
- (b) Name any two materials from the list that will make the bulb glow.
- (c) What do we call materials that do not allow current to pass and keep the bulb off?
- (d) Why is this tester activity useful for students?
Answers:
(a) The bulb will glow when conductors are placed between the tester ends.
(b) Copper wire and aluminium foil are conductors and will make the bulb glow.
(c) Such materials are called insulators, e.g. plastic scale and rubber piece.
(d) It helps students identify conductors and insulators and understand which materials allow current to pass.
Case 11 – Wet Hands near Switch:
Suman is about to switch on the bathroom light with wet hands after washing her face. Her mother quickly stops her and explains why it can be dangerous to touch switches with wet hands.
- (a) Why should we not touch electrical switches with wet hands?
- (b) Is pure distilled water a good conductor of electricity?
- (c) Why does ordinary tap water conduct electricity better than distilled water?
- (d) Mention one safety rule you follow at home related to electricity.
Answers:
(a) Because water with dissolved salts acts as a conductor and can allow current through our body, causing electric shock.
(b) No, pure distilled water is a poor conductor of electricity.
(c) Tap water has dissolved salts and impurities which provide ions to carry electric current.
(d) Example: Never insert metal objects into plug points; never overload sockets; always switch off main supply before repairs (any one).
Case 12 – Insulated Tools:
An electrician comes to repair a fan in Arun’s house. Arun notices that the electrician’s tools such as screwdrivers and pliers have metal tips but plastic handles. Curious, he asks why these handles are made of plastic.
- (a) What type of material is used for the handles of these tools?
- (b) Why is plastic suitable for handles of electrical tools?
- (c) What would happen if the handles were made only of metal?
- (d) Which part of the tool needs to be a conductor and why?
Answers:
(a) The handles are made of plastic, which is an insulator.
(b) Plastic does not allow current to pass through, so it protects the electrician from electric shocks.
(c) If handles were only metal, current could pass into the electrician’s body and cause shock or injury.
(d) The tip or working end of the tool should be a conductor so that it can make proper contact with wires and terminals.
Topic 5: Switches, Circuit Symbols & Diagrams
Case 13 – Drawing a Circuit Diagram:
A teacher draws a picture of a real circuit on the board showing a cell, connecting wires, a bulb and a switch. Then she asks students to draw a neat circuit diagram using symbols instead of detailed pictures.
- (a) What is a circuit diagram?
- (b) Why do we use standard symbols in circuit diagrams?
- (c) How is a cell represented in a circuit diagram?
- (d) How is a closed switch shown differently from an open switch?
Answers:
(a) A circuit diagram is a simple drawing of an electric circuit using standard symbols for components.
(b) Symbols make the diagram easy to draw and understand, and the same symbols are understood by everyone.
(c) A cell is shown by two parallel lines: a longer line for the positive terminal and a shorter line for the negative terminal.
(d) A closed switch is shown as a straight line without a gap, while an open switch is shown with a gap in the line.
Case 14 – Correct Position of Switch:
In a circuit diagram, Neha draws the switch in parallel with the bulb instead of in series. When she makes this circuit on the board with actual wires, she finds that closing the switch does not make the bulb glow.
- (a) Where should a switch ideally be placed in a simple circuit with one bulb?
- (b) What happens if the switch is connected in parallel with the bulb?
- (c) Will current find an easier path through the switch or through the bulb? Why?
- (d) How can Neha correct her circuit to make the bulb glow when the switch is ON?
Answers:
(a) The switch should be placed in series with the bulb.
(b) In parallel, the switch provides another path that can bypass the bulb.
(c) Current will mainly pass through the switch because it offers almost no resistance, so the bulb may not glow.
(d) She should connect the switch in series so that the same current passes through the switch and the bulb.
Case 15 – Direction of Current in a Diagram:
A student draws arrows in a circuit diagram from the negative terminal of a cell to the positive terminal and labels it “direction of current”. The teacher corrects him and explains conventional current direction.
- (a) In which direction is conventional current taken to flow in a circuit?
- (b) From which terminal to which terminal should the arrows be drawn?
- (c) Why is it important to follow a common convention for the direction of current?
- (d) Does the actual flow of electrons occur in the same or opposite direction to conventional current?
Answers:
(a) Conventional current is taken to flow from the positive terminal to the negative terminal of a cell.
(b) Arrows should be drawn from the positive terminal, through the circuit, towards the negative terminal.
(c) A common convention helps everyone understand and communicate circuit behaviour in the same way.
(d) The actual flow of electrons is in the opposite direction, but at this level we use conventional current direction.
Topic 6: Series & Parallel, Heating Effect, Fuse & Safety
Case 16 – Two Bulbs in Series:
In a classroom activity, two identical bulbs are connected in series with a cell. The bulbs glow dimly compared to when only one bulb is connected. When one bulb is removed, the other also goes off.
- (a) What do we mean by series connection of bulbs?
- (b) Why do the bulbs glow dimmer in series than a single bulb?
- (c) Why does the other bulb go off when one bulb is removed?
- (d) Is series connection suitable for house wiring? Give one reason for your answer.
Answers:
(a) Series connection means the bulbs are connected one after another in a single path for current.
(b) The total resistance increases, so less current flows, making both bulbs glow dimmer.
(c) Removing one bulb breaks the circuit, so current stops and the other bulb also goes off.
(d) No, because if one appliance fails, all in series stop working; this is inconvenient for homes.
Case 17 – Parallel Connection at Home:
In Ritu’s house, if one tube light fuses, the fans and other lights still work. Her teacher explains that this is because electrical appliances at home are generally connected in parallel.
- (a) What is a parallel connection?
- (b) Why do other appliances keep working when one bulb fuses in a parallel circuit?
- (c) Mention one advantage of using parallel connection in homes.
- (d) Why can each appliance in a parallel connection be controlled by a separate switch?
Answers:
(a) In parallel connection, appliances are connected in separate branches between the same two points in the circuit.
(b) Each appliance has its own path; if one path is broken, current can still flow through the other branches.
(c) Each appliance gets the same voltage and can work independently; failure of one does not affect others.
(d) Because each branch has its own switch, closing or opening that switch controls only the appliance in that branch.
Case 18 – Electric Iron:
An electric iron is used at home to press clothes. When it is switched on, after a few minutes it becomes hot. There is also a small light which glows when the iron is heating. Inside, it has a coil-like heating element.
- (a) Which effect of electric current is used in an electric iron?
- (b) What happens inside the heating element when current flows through it?
- (c) Why should we not touch the metal base of the iron when it is ON?
- (d) Mention one safety precaution to follow while using an electric iron.
Answers:
(a) The heating effect of electric current is used.
(b) The high-resistance element converts electrical energy into heat energy and becomes very hot.
(c) The base becomes very hot and can burn our skin, so we should not touch it.
(d) Always switch off the iron when not in use and keep it upright on a stand; check that the wire and plug are not damaged.
Case 19 – Fuse Wire Melts:
In a house, too many appliances are connected to a single plug point. Suddenly, all the appliances stop working and the people notice that the fuse in the main board has melted. After replacing the fuse, everything works normally again.
- (a) What is an electric fuse?
- (b) Why did the fuse wire melt when many appliances were connected?
- (c) How does a fuse protect the household wiring?
- (d) Why should we avoid overloading a plug point with too many appliances?
Answers:
(a) A fuse is a safety device with a thin wire that melts and breaks the circuit if too much current flows.
(b) Many appliances drew a very large current, which heated the fuse wire beyond its melting point.
(c) By melting and breaking the circuit, it stops the flow of excess current and protects wires and appliances from damage and fire.
(d) Overloading increases current beyond safe limits and can cause overheating, fire and appliance damage.
Case 20 – Safety at School Lab:
During a practical class on electricity, the science teacher reminds students not to use the mains supply for experiments. Instead, they must use only dry cells. She also tells them not to play with switches and sockets in the lab.
- (a) Why are dry cells used in school experiments instead of mains electricity?
- (b) What danger is involved in using mains supply carelessly?
- (c) Mention two safety rules students should follow in the science lab while doing electrical experiments.
- (d) Why is it important to learn about electrical safety at a young age?
Answers:
(a) Dry cells provide a low and safer voltage of electricity suitable for small experiments.
(b) Mains supply carries high voltage and can cause severe electric shocks and fire if used carelessly.
(c) Examples: (i) Do not touch switches, plugs or wires with wet hands. (ii) Do not insert objects into sockets or play with wiring.
(d) Learning safety early helps students avoid accidents at home and school and teaches them to handle electricity responsibly.