Class 7 Science Curiosity Chapter 3 MCQ – Electricity: Circuits and their Components

A switch controls whether a circuit is complete or broken; it does not supply electrical energy. The cell or battery is the source. Closing the switch can allow current to flow, while opening it interrupts the path.

The metal ends of connecting wires must touch the terminals to provide a conducting path. If insulating material remains between them, the path is interrupted. A working cell and lamp alone cannot overcome this missing electrical connection.

An electric cell provides electrical energy in a form that can be carried from place to place. This is why cells are useful in devices such as torchlights and clocks, where a connection to a wall socket is unnecessary.

The chapter identifies the small protruding metal cap of the cylindrical cell as its positive terminal. The flat metal disc forms the negative terminal. Recognising these parts helps us connect cells and other circuit components in the intended order.

The battery arrangement described joins the positive terminal of one cell to the negative terminal of the next. Connecting cells in the correct order is important; merely placing several cells near one another does not create the required arrangement.

The filament is the thin wire inside an incandescent lamp. When electric current passes through it, the filament becomes hot and gives out light. It must remain unbroken so that current can pass through the lamp’s internal path.

One supporting wire connects the filament to the metal case, while another connects it to the metal tip at the base. These two separate terminals allow current to enter and leave the filament when the lamp is correctly connected.

LED stands for Light Emitting Diode. The chapter explains that many modern torches use LEDs instead of incandescent lamps. An LED gives light without having the glowing filament found inside the older type of torch lamp.

The longer wire of the LED is its positive terminal, and the shorter wire is its negative terminal. These markings matter because an LED must be connected in the correct direction for current to pass through it and produce light.

An LED allows current to pass through it in only one direction. Its positive lead must connect towards the battery’s positive terminal and its negative lead towards the negative terminal. Reversing these connections prevents it from glowing in the activity.

A lamp glows when current passes through it in a complete circuit. Both lamp terminals must be connected appropriately to the source. A missing connection or an open gap interrupts the path and prevents the required current flow.

The chapter uses the accepted direction of electric current from the cell’s positive terminal to its negative terminal through the external circuit. The path must be complete so that current passes through components such as the connected lamp.

A broken filament creates a gap inside the lamp. This stops electric current from passing through the filament, even if the external connections appear correct. The lamp is then commonly described as fused and needs to be replaced.

In the OFF position, the safety pin does not touch the second drawing pin. This leaves a gap in the conducting path. The circuit is open, so current does not pass through the lamp and it remains off.

The longer line represents the positive terminal of the cell, while the shorter line represents the negative terminal. These symbols simplify circuit drawings and help readers identify the source’s connections without drawing the actual shape of the cell.

The two arrows indicate that the LED emits light. They help distinguish its symbol from those of other circuit components. The chapter uses standard symbols so that an electrical circuit can be represented and understood more easily.

Plastic, rubber, and ceramics are named as electrical insulators. They do not let current pass through easily and are useful as protective coverings. Conducting metal parts carry current, while insulating parts help prevent people from touching those conducting paths.

Copper is a good conductor and is comparatively less costly and more readily available than silver or gold. These practical advantages make it useful for electrical wires, even though other metals also conduct electricity very well.

The chapter explains that batteries usually supply direct current, called DC. It contrasts this with alternating current, or AC, supplied through wall sockets. For classroom investigations, the chapter uses cells and batteries as the electrical energy sources.

Electrical conductors allow current to flow through them easily. The chapter uses a tester with a cell and lamp to investigate this property. When an appropriate conducting material completes the gap, the lamp can glow in the circuit.

The connection already uses the positive terminal of P and the negative terminal of Q. Each cell has one terminal left unused. These are P’s negative terminal and Q’s positive terminal, which form the free ends of the combined source.

An LED depends on the direction of its connection. Reversing the leads can place its longer positive lead towards the battery’s positive terminal and its shorter negative lead towards the negative terminal, allowing current to pass in the correct direction.

Unlike the LED described in the chapter, an incandescent lamp does not need a particular terminal direction. Current can heat its filament with either connection to the cell, provided the circuit remains complete and the components are working.

The chapter explains that a switch can be placed anywhere in a simple circuit. Its purpose is to complete or interrupt the path. Moving it does not change that purpose when the circuit is connected correctly.

The chapter identifies wood as a poor conductor of electricity in the tester activity. Replacing a conducting metal key with dry wood prevents an easy path for current through the gap, so the tester’s lamp does not glow.

The tester is meant to find out whether the object conducts electricity. If the wire ends touch each other directly, they may complete the path without using the object. Separate contact points make the object part of the tested path.

Both lamps share one current path in the single loop described. A broken filament interrupts that path, so current cannot pass through either lamp. This follows the chapter’s rule that a glowing lamp requires a complete electrical circuit.

An open switch anywhere in a single loop leaves a gap in the path. Closing only one of two switches is therefore insufficient. Both switches must complete their parts of the circuit before current can pass through the lamp.

The longer LED lead is its positive terminal. In the chapter’s circuit, the LED glows when that lead connects towards the battery’s positive terminal. Observing the successful connection can therefore help identify the battery terminal whose sign is missing.

Only the cell was changed between the two tests. Because the same lamp and connections work with the replacement cell, the original cell is the likely cause of the failure. Changing one part makes the comparison useful.