Electricity: Circuits and their Components — Mastery

Q1. Which of the following is NOT placed under the 'Cooking' heading in the chapter's grouping of uses of electricity?

• A. Electric kettle
• B. Mixer grinder
• C. Toaster
• D. Refrigerator

Q2. Under which heading does the chapter place 'fan, room heater, immersion rod, geyser, refrigerator and air conditioner'?

• A. Communication
• B. Cooking
• C. Others
• D. Heating and Cooling

Q3. Among the following, which group is grouped together under 'Transportation' in the chapter?

• A. Train, bus, car, scooter, lift, escalator
• B. Television, radio, computer
• C. Water pump, crane, geyser
• D. Mobile phone, Internet, microwave

Q4. The danger signs printed on electric poles and other electrical appliances warn people that

• A. Electricity is always safe if the device looks new
• B. Only adults can see electricity
• C. Electricity can be dangerous if not carefully handled
• D. Electricity only flows during the day

Q5. The chapter's caution on safety adds that even electricity from a portable generator

• A. Is completely safe and may be used for student experiments
• B. Is exactly the same as that from a battery
• C. Has no positive or negative terminal
• D. Can be dangerous and should not be used for student experiments

Q6. A torchlight is also known by which of these names in the chapter?

• A. Torch or flashlight
• B. Periscope or telescope
• C. Geyser or boiler
• D. Filament or fuse

Q7. When Activity 3.1 asks a Class 7 student to open a torchlight, what is the student likely to find inside?

• A. Two or more electric cells
• B. A laboratory thermometer with mercury
• C. A pair of magnetic poles
• D. A small refrigerator

Q8. On an ordinary electric cell, the negative terminal is the

• A. Small protruding metal cap on one side
• B. Glass dome at the top
• C. Flat metal disc on the other side
• D. Paper label printed on the body

Q9. If the '+' and '−' symbols are no longer legible on a battery and you must still identify its two terminals, the chapter's exercise suggests

• A. Cutting the battery open to look inside
• B. Heating the battery on a flame to see colour changes
• C. Designing a simple activity that uses a known cell and a lamp/LED to test the connection
• D. Weighing each end of the battery on a balance

Q10. Why do many devices use more than one cell joined as a battery rather than a single cell?

• A. Because more cells make the device lighter
• B. Because a battery is required by law for any electrical activity
• C. Because connecting more than one cell provides energy to the circuit for a longer time and/or more energy
• D. Because a single cell cannot fit inside any device

Q11. Inside a battery compartment where the cells are placed side by side, a thick wire or metal strip connects the positive terminal of one cell to the negative terminal of the next. Why is this strip needed?

• A. Only to hold the cells in place mechanically
• B. To complete the battery connection by joining the cells in the correct positive-to-negative order
• C. To insulate the cells from each other
• D. To convert DC into AC

Q12. In an incandescent lamp, light is produced when

• A. The glass bulb cools down rapidly
• B. Air inside the bulb evaporates
• C. The metal case is rubbed with a cloth
• D. The filament gets hot and glows due to the current passing through it

Q13. Inside an incandescent lamp, the two thick supporting wires that lead to the filament are arranged so that

• A. They touch each other to share current
• B. They cross over each other for support
• C. They do not touch each other, so that the two terminals of the lamp remain separate
• D. They are coated with mercury

Q14. Unlike an incandescent lamp, an LED

• A. Has no filament inside
• B. Has a much thicker filament
• C. Always has three terminals
• D. Glows only when warmed by hand

Q15. A modern torchlight that uses LEDs may carry

• A. Always exactly one red LED
• B. Always exactly one white LED
• C. One or more LEDs, sometimes of different shapes and colours
• D. An LED that is also a battery

Q16. In Activity 3.6, what is the role of the two wires attached to the two ends of the cell holder?

• A. They store extra current as a backup
• B. They protect the cell from sunlight
• C. They form the leads through which the cell is connected to the rest of the circuit
• D. They make the holder waterproof

Q17. If a cell holder is not available in the school lab, the chapter suggests that the two wires should be fixed to the cell using

• A. Cellotape and a paper clip
• B. Insulating clay
• C. Wax from a candle
• D. Electrical tape, in place of the cell holder

Q18. When using a lamp holder in Activity 3.6, the two wires are attached to the holder at

• A. The screws of the lamp holder
• B. The plastic body of the holder
• C. The glass bulb of the lamp
• D. The bottom of the cell

Q19. In a completed torch circuit, the incandescent lamp glows only as long as

• A. Current keeps passing through the filament
• B. The lamp is wrapped in cloth
• C. The cell holder is shaken continuously
• D. Sunlight falls on the bulb

Q20. Ravi closes the switch of a torch with an incandescent lamp and observes the lamp glow. Which sequence correctly traces the path of current in the closed circuit?

• A. Lamp → switch → cell (negative to positive) → wire → back to lamp
• B. Wire → glass bulb → wire → metal case → wire → metal tip → wire → cell
• C. Switch → lamp → switch → lamp → switch → cell
• D. Cell (positive) → wire → switch → filament of the lamp → wire → back to negative of cell

Q21. When the chapter says an incandescent lamp has 'fused', it most directly means

• A. Its glass bulb has melted
• B. Its metal cap has fallen off
• C. Its base has been painted
• D. Its filament has broken

Q22. The chapter advises: 'Always take care to connect an LED correctly in a circuit to make it glow.' The correctness referred to here is

• A. Length of the wires used in the circuit
• B. Colour of the LED
• C. Brand of the battery
• D. Direction of the LED — its longer wire must meet the battery's positive terminal

Q23. How does the safety-pin-and-drawing-pin switch built in Activity 3.8 compare with the switch used for a light in your home?

• A. It is the same in working principle (completing or breaking a circuit), though household switches are designed differently
• B. It is completely unrelated — household switches work on magnetism, not on contact
• C. It uses AC, while household switches use only DC
• D. It cannot turn a lamp on, only off

Q24. Where in a simple single-loop circuit can a switch be placed so that it controls the lamp?

• A. Only directly next to the positive terminal of the cell
• B. Only directly next to the lamp
• C. Anywhere in the circuit — the lamp glows or stays off depending on whether the switch is ON or OFF
• D. Only outside the circuit

Q25. In Table 3.2, the symbol used for a battery (rather than a single cell) is drawn as

• A. A circle with a cross through it
• B. A triangle with two arrows
• C. Two single-cell symbols placed next to each other and joined
• D. A single pair of long and short lines

Q26. Among the standard symbols in Table 3.2, the symbol drawn as a circle with a cross inside it represents

• A. An LED
• B. A switch in 'OFF' position
• C. A wire
• D. An incandescent electric lamp

Q27. In Activity 3.11, a tester is built by connecting an electric cell and a lamp while leaving the two ends of the wires free. When the two free ends are touched to a wooden stick, the lamp does not glow. What does this observation tell the student?

• A. Wood is an electrical insulator and does not let current pass
• B. The cell is dead
• C. The lamp is fused
• D. The lamp must be made of wood to glow

Q28. Although silver, copper and gold are all listed as the best electrical conductors, the chapter explains that copper is mainly used for making electrical wires. Which is the best justification?

• A. Copper is shinier than silver and gold
• B. Copper is heavier and so safer to handle than silver and gold
• C. Copper has comparatively lower cost and abundant supply, making it practical for large-scale wiring
• D. Copper is the only metal that does not get hot

Q29. A teacher finds that several students in her Class 7 say 'the switch is the source of electricity in a torch'. Which of the following is the MOST effective way to address this misconception?

• A. Tell the students they are wrong and move on to the next chapter
• B. Set up the safety-pin switch with a cell and lamp, remove the cell while leaving the switch ON, and ask the students to predict and observe whether the lamp now glows
• C. Have the students copy the definition of 'switch' from the board ten times
• D. Show the students a video of a hydroelectric power station

Q30. Before students fill in Table 3.1 (six cell-and-lamp arrangements), the chapter directs them to 'predict, for each arrangement, if the lamp will glow or not'. From a pedagogy point of view, the BEST reason to insist on prediction before observation is that

• A. It saves time during the class
• B. It surfaces students' existing mental model so that the later observation either confirms it or corrects it, making learning durable
• C. It allows the teacher to grade the students before the activity
• D. It prevents students from speaking during the activity