Electricity: Circuits and their Components
Chapter 3, 'Electricity: Circuits and their Components,' introduces students to the basics of electricity. It covers the structure and function of electric cells, how to form a battery, the components of an electric lamp (incandescent and LED), and the concept of an electrical circuit. Students learn about switches, circuit diagrams, and the crucial distinction between electrical conductors and insulators. Understanding these concepts is vital for comprehending how everyday electrical devices work and for building a strong foundation in physics.
Easy (15)
- Which part of an electric cell is considered its positive terminal?
- Metal disc
- Metal cap (correct)
- Plastic casing
- Insulating layer
Why: The metal cap of an electric cell is its positive terminal.
- What is the glowing thin wire inside an incandescent lamp called?
- Conductor
- Insulator
- Filament (correct)
- Terminal
Why: The glowing thin wire inside an incandescent lamp is called the filament.
- A combination of two or more electric cells is known as a:
- Circuit
- Battery (correct)
- Switch
- Lamp
Why: A battery is formed by combining two or more electric cells.
- Which of the following materials is a good conductor of electricity?
- Rubber
- Plastic
- Wood
- Metal (correct)
Why: Metals are generally good conductors of electricity.
- What is the primary function of an electric switch?
- To generate electricity
- To store electricity
- To complete or break a circuit (correct)
- To convert electrical energy into light
Why: An electric switch's main role is to complete or break a circuit.
- In an electrical circuit, the direction of current is conventionally taken from:
- Negative to positive terminal
- Positive to negative terminal (correct)
- Both directions simultaneously
- It depends on the type of circuit
Why: Current direction is from positive to negative terminal.
- Which component is represented by a long line and a short line in a circuit diagram?
- Electric lamp
- Electric cell (correct)
- Switch
- Wire
Why: An electric cell is represented by a long and a short line in a circuit diagram.
- What is the purpose of the plastic or rubber covering on electrical wires?
- To make them look attractive
- To increase their flexibility
- To protect people from electric shocks (correct)
- To make them stronger
Why: Plastic/rubber covers on wires act as insulators to prevent electric shocks.
- True or False: An LED (Light Emitting Diode) has a filament inside it, similar to an incandescent lamp.
Why: LEDs do not have filaments.
- True or False: An electric cell is a portable source of electrical energy.
Why: Electric cells are indeed portable sources of electrical energy.
- True or False: In an incandescent lamp, the lamp will glow regardless of which terminal connects to the positive or negative terminal of the cell, as long as the circuit is complete.
Why: Incandescent lamps glow as long as the circuit is complete, irrespective of terminal connection polarity.
- A setup that provides a complete path for electric current to flow through a lamp is called an electrical _________.
Why: A complete path for current is an electrical circuit.
- Materials through which current cannot pass are called __________.
Why: Materials blocking current flow are insulators.
- Identify the positive terminal of the electric cell in the given diagram.
- A (Metal disc)
- B (Metal cap) (correct)
- C (Side casing)
- D (Bottom insulator)
Why: The metal cap (B) is the positive terminal.
- Which part of the incandescent lamp shown in the diagram is the filament?
- A (Glass bulb)
- B (Thick wire)
- C (Filament) (correct)
- D (Metal tip)
Why: C points to the thin, coiled wire, which is the filament.
Medium (15)
- Why does an LED only glow when connected in a specific direction (positive to positive, negative to negative)?
- It has a special type of filament that requires specific polarity.
- It is designed to allow current to pass through in one direction only. (correct)
- Its resistance changes with the direction of current.
- It needs to be protected from overheating.
Why: LEDs are diodes, allowing current flow in only one direction.
- You have two electric cells. To form a battery, how should you connect their terminals?
- Positive to positive, negative to negative
- Positive to negative, negative to positive (correct)
- Any way, as long as they are touching
- Only the positive terminals need to be connected
Why: For a battery, connect positive terminal of one cell to negative of the next.
- If you replace the incandescent lamp in a torch with an LED lamp, what change might you observe regarding its terminals?
- The LED lamp will have only one terminal.
- The LED lamp will have two terminals of equal length.
- The LED lamp will have two terminals of different lengths (one longer, one shorter). (correct)
- The LED lamp will not have any visible terminals.
Why: LEDs have distinct longer (positive) and shorter (negative) terminals.
- Why are electrical wires typically made of metals like copper, but covered with materials like plastic or rubber?
- Metals are cheap, and plastic/rubber makes them look better.
- Metals are conductors, and plastic/rubber are insulators. (correct)
- Metals are strong, and plastic/rubber makes them flexible.
- Metals prevent corrosion, and plastic/rubber prevents overheating.
Why: Metals conduct electricity, while plastic/rubber insulate, ensuring safety.
- Match the electrical component with its correct function.
Why: Each component has a specific role in an electrical system.
- Match the material with its electrical property.
Why: Materials are classified as conductors or insulators based on current flow.
- Match the terminal type with its characteristic in an electric cell.
Why: Electric cells and LEDs have distinct positive and negative terminals.
- Match the circuit state with its outcome.
Why: Circuit states directly determine if a lamp glows.
- The representation of an electrical circuit using symbols is called a circuit _________.
Why: A circuit diagram uses symbols to represent electrical components.
- What is the term for materials through which electric current cannot pass?
Why: Insulators block the flow of electric current.
- What is the name given to the small protruding metal cap on one side of an electric cell?
Why: The metal cap is the positive terminal.
- Arrange the steps to make an incandescent lamp glow using an electric cell in the correct sequence.
Why: A complete circuit is needed for the lamp to glow.
- Arrange the steps for testing a material's conductivity using a simple tester.
Why: The tester checks if a material completes the circuit, allowing the lamp to glow.
- In the given circuit diagram, what does the component labeled 'X' represent?
- Electric cell
- Electric lamp (correct)
- Switch in 'ON' position
- Battery
Why: The circular symbol with a cross represents an electric lamp.
- Observe the circuit diagram. What does the symbol indicated by 'Y' signify?
- Electric cell
- Switch in 'OFF' position (correct)
- Battery
- Wire
Why: Symbol 'Y' represents an open switch, meaning it's in the 'OFF' position.
Hard (10)
- Assertion (A): Electrical wires are covered with plastic or rubber. Reason (R): Plastic and rubber are good conductors of electricity.
Why: Plastic/rubber are insulators, not conductors, protecting from shocks.
- Assertion (A): An LED (Light Emitting Diode) will glow even if its longer wire is connected to the negative terminal and shorter wire to the positive terminal of a battery. Reason (R): LEDs are designed to allow current to flow in both directions.
Why: LEDs only glow when connected correctly (longer wire to positive, shorter to negative) because current flows in one direction only.
- Assertion (A): In a torch, multiple cells are often arranged in a specific order. Reason (R): This specific order ensures that the positive terminal of one cell connects to the negative terminal of the next, forming a battery to provide sufficient voltage.
Why: Cells in a torch are arranged positive-to-negative to form a battery, which is essential for its operation.
- A student is trying to make a lamp glow using a cell, wires, and a switch. They connect the components as shown in the diagram. However, the lamp does not glow. Which of the following is the most likely reason for the lamp not glowing?
- The cell is dead or discharged.
- The switch is in the 'OFF' position. (correct)
- The lamp's filament is broken.
- The wires are too long.
Why: The diagram shows the switch in the 'OFF' position, creating an open circuit.
- A technician is testing different materials using a conduction tester (similar to Fig. 3.15). The tester's lamp glows when a metal key is placed between the free ends, but does not glow when a wooden stick is placed. What can be concluded from these observations?
- Both metal and wood are good conductors of electricity.
- Metal is a good conductor, while wood is an insulator. (correct)
- Both metal and wood are insulators of electricity.
- The tester is faulty, as wood should also make the lamp glow.
Why: The lamp glowing for metal means it's a conductor; not glowing for wood means it's an insulator.
- A student connects an LED to a battery using wires. The LED does not glow. Upon checking, the student finds that the longer wire of the LED is connected to the negative terminal of the battery, and the shorter wire is connected to the positive terminal. What is the most appropriate action for the student to take to make the LED glow?
- Increase the number of cells in the battery.
- Replace the LED with an incandescent lamp.
- Reverse the connections of the LED wires to the battery terminals. (correct)
- Use thicker wires for the connections.
Why: LEDs are polarity-sensitive; reversing the incorrect connections will make it glow.
- Observe the circuit diagram. If the switch is closed, which component would allow current to flow through it?
- The air gap around the lamp
- The glass bulb of the lamp
- The connecting wires (correct)
- The insulating material of the cell
Why: Connecting wires are conductors, allowing current flow in a closed circuit.
- Consider the circuit diagram with an LED. If the cell's positive terminal is connected to the LED's shorter wire and the negative terminal to the LED's longer wire, what will happen?
- The LED will glow brightly.
- The LED will glow dimly.
- The LED will not glow. (correct)
- The LED might get damaged.
Why: Reverse polarity connection prevents the LED from glowing.
- Which of the following statements are TRUE regarding an electric cell and an LED?
- The metal cap of an electric cell is its positive terminal. (correct)
- An LED has a filament that heats up to produce light.
- The longer wire of an LED is its positive terminal. (correct)
- An electric cell converts light energy into electrical energy.
Why: Electric cells have a positive metal cap; LEDs have a longer positive wire and no filament.
- Which two of the following are essential conditions for an incandescent lamp to glow in a circuit?
- The circuit must be complete (closed). (correct)
- The lamp's filament must be intact. (correct)
- The lamp must be connected with its positive terminal to the cell's positive terminal.
- The circuit must contain an LED.
Why: A complete circuit and an intact filament are necessary for an incandescent lamp to glow.
