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Q1. An electric circuit includes
An electric circuit includes a cell (or battery) as the source of electricity, a plug key (switch) to make or break the circuit, various components (like bulbs, resistors, ammeters), and connecting wires. All these are connected in a closed loop to allow current to flow. A circuit cannot function with just one component.
Q2. Mathematical form of Ohm’s law is
Ohm’s law states that the potential difference (V) across a conductor is directly proportional to the current (I) flowing through it, provided the temperature remains constant. Mathematically, V = IR, where R is the resistance of the conductor. This is one of the most fundamental laws in electricity.
Q3. The relationship between current and potential difference was given by
The relationship between current and potential difference was given by Georg Simon Ohm, a German physicist. He discovered that for a metallic conductor at constant temperature, the current is directly proportional to the potential difference. This relationship is now known as Ohm’s law and was published in 1827.
Q4. In Activity 3.2, four cells are connected in
In Activity 3.2, four cells are connected in series to study the variation of current with potential difference. When cells are connected in series, the total potential difference is the sum of the individual cell voltages (e.g., 4 cells × 1.5 V = 6 V). This arrangement allows students to observe how current changes with voltage.
Q5. In Ohm’s law experiment, current is measured using
In Ohm’s law experiment, current is measured using an ammeter. An ammeter is always connected in series with the circuit so that all the current passes through it. It has very low resistance so it does not affect the current being measured. The ammeter readings are recorded for different voltages.
Q6. Potential difference of 1 V means
Potential difference of 1 volt means that 1 joule of work is done to move 1 coulomb of charge from one point to another. Mathematically, V = W/Q, where V is potential difference, W is work done, and Q is charge. So, 1 V = 1 J/1 C = 1 J C⁻¹.
Q7. Work done in moving a charge of 2 C across 12 V is
Work done W = V × Q = 12 V × 2 C = 24 J. The formula for work done in moving a charge is W = VQ, where V is the potential difference and Q is the charge. So, for a charge of 2 coulombs across a potential difference of 12 volts, the work done is 24 joules.
Q8. Formula for potential difference is
The formula for potential difference is V = W/Q, where V is the potential difference, W is the work done (in joules), and Q is the charge (in coulombs). This formula defines potential difference as the work done per unit charge to move a charge between two points.
Q9. Potential difference is measured using
Potential difference is measured using a voltmeter. A voltmeter is always connected in parallel across the two points where the potential difference is to be measured. It has very high resistance so it draws negligible current from the circuit and does not affect the measurement.
Q10. Potential difference is measured using
Potential difference is measured using a voltmeter (same as Q9). A voltmeter is connected in parallel and has high resistance. It measures the voltage between two points in a circuit without significantly altering the current. The unit of measurement is volts (V).
Q11. The constant ratio V/I is called
The constant ratio V/I is called resistance. According to Ohm’s law, for a given conductor at constant temperature, the ratio of potential difference (V) to current (I) is constant. This constant is the resistance (R) of the conductor. Resistance is a measure of how much a conductor opposes the flow of current.
Q12. Electric potential difference is defined as
Electric potential difference is defined as the work done per unit charge to move a charge from one point to another. Mathematically, V = W/Q. It is also called voltage. The SI unit of potential difference is the volt (V), where 1 V = 1 J/C.
Q13. Circuit symbols are used because they are
Circuit symbols are used because they are easier and more convenient to draw than actual physical representations of components. Standard symbols for cells, bulbs, resistors, switches, ammeters, and voltmeters are used in schematic diagrams to clearly and quickly represent circuits without drawing detailed pictures.
Q14. In V–I graph, the graph obtained is
In a V–I graph, the graph obtained is a straight line passing through the origin. This shows that the potential difference (V) is directly proportional to the current (I), which is Ohm’s law. The slope of the line gives the resistance (R = V/I) of the conductor. This linear relationship holds true for metallic conductors at constant temperature.
Q15. Potential difference in a circuit is produced by
Potential difference in a circuit is produced by a battery or cell. The battery converts chemical energy into electrical energy, creating a potential difference between its terminals. This potential difference drives the current through the circuit. Other devices like ammeters and voltmeters measure current and voltage, they do not produce potential difference.
Q16. Torch bulb is used in Activity 3.2 to
A torch bulb is used in Activity 3.2 to increase resistance in the circuit. The bulb acts as a resistor. By using a bulb, students can observe how adding resistance affects the current in the circuit. The bulb also serves as an indicator of current flow—if the bulb glows, current is flowing.
Q17. A device that maintains potential difference across a conductor is
A device that maintains potential difference across a conductor is a cell or battery. The cell provides a constant potential difference (voltage) across its terminals, which drives the current through the circuit. Ammeters measure current, switches control the circuit, and bulbs are loads that convert electrical energy to light.
Q18. Ohm’s law relates
Ohm’s law relates voltage (V), current (I), and resistance (R). It states that V = IR, where V is the potential difference, I is the current, and R is the resistance. This law describes the fundamental relationship between these three quantities in an electrical circuit. It is one of the most important laws in electricity.
Q19. A voltmeter is always connected in
A voltmeter is always connected in parallel across the two points where the potential difference is to be measured. It has very high resistance so that it draws negligible current from the circuit. This ensures accurate measurement without affecting the circuit’s operation. Parallel connection allows the voltmeter to measure the voltage across a specific component.
Q20. According to Ohm’s law
According to Ohm’s law, the potential difference (V) is directly proportional to the current (I) flowing through a conductor, provided the temperature and other physical conditions remain constant. This means V ∝ I, or V = IR. So, for a fixed resistance, increasing the voltage increases the current proportionally.
Q21. Ohm’s law applies to
Ohm’s law applies to metallic conductors (like copper, aluminum, and iron) at constant temperature. It is valid for most metals and alloys. However, it does not apply to all materials. Semiconductors (like silicon, germanium) and insulators do not follow Ohm’s law as their resistance changes with voltage and temperature.
Q22. Ohm’s law is valid when
Ohm’s law is valid when the temperature of the conductor remains constant. If the temperature changes, the resistance of the conductor also changes, and Ohm’s law no longer applies. This is why Ohm’s law is stated with the condition that physical conditions (like temperature) remain unchanged.
Q23. Resistance is the property of a conductor to
Resistance is the property of a conductor to resist the flow of electric charges (current). It is a measure of how much a conductor opposes the flow of electrons. Higher resistance means more opposition to current flow. The SI unit of resistance is the ohm (Ω). Resistance depends on the material, length, and cross-sectional area of the conductor.
Q24. To maintain electric current, a cell uses its
To maintain electric current, a cell uses its chemical energy. A cell converts chemical energy into electrical energy through chemical reactions between the electrolyte and electrodes. This chemical energy creates a potential difference between the terminals, which drives the current through the circuit. This is why batteries are often called chemical cells.
Q25. One volt is equal to
One volt is equal to 1 joule per coulomb (1 J/C). This means that when 1 joule of work is done to move 1 coulomb of charge between two points, the potential difference is 1 volt. The volt is the SI unit of potential difference and is named after the Italian physicist Alessandro Volta.
Q26. The SI unit of resistance is
The SI unit of resistance is the ohm (symbol Ω). It is named after the German physicist Georg Simon Ohm. One ohm is the resistance of a conductor when a potential difference of 1 volt produces a current of 1 ampere. The ohm is a derived SI unit.
Q27. After measuring current, the key should be
After measuring current, the key (switch) should be removed or opened to break the circuit. This prevents the battery from draining and protects the components from continuous current flow. It is a good practice to open the circuit when measurements are not being taken to avoid unnecessary power consumption and heating.
Q28. The formula used to calculate work done is
The formula used to calculate work done (in moving a charge) is W = VQ, where W is work done, V is the potential difference, and Q is the charge. This formula comes from the definition of potential difference: V = W/Q, so W = VQ. Work done is measured in joules (J).
Q29. Nichrome is an alloy of
Nichrome is an alloy of nickel, chromium, manganese, and iron. It is widely used as a heating element in electric appliances because it has high resistance and does not oxidize easily at high temperatures. Nichrome can withstand high temperatures without melting, making it ideal for heaters, toasters, and hair dryers.
Q30. Increasing number of cells increases
Increasing the number of cells connected in series increases the potential difference (voltage). Each cell provides a certain voltage (e.g., 1.5 V). When cells are connected in series, their voltages add up. For example, 4 cells of 1.5 V each give a total voltage of 6 V. This increases the potential difference driving the current.
Q31. Volt is named after
Volt is named after Alessandro Volta (1745–1827), an Italian physicist who invented the Voltaic pile, the first electric battery. The unit of potential difference was named in his honour. He made significant contributions to the study of electricity and electrochemistry.
Q32. A battery consists of
A battery consists of one or more electric cells connected together. When multiple cells are connected, they are called a battery. A battery can provide a higher voltage or higher capacity than a single cell. For example, a 9V battery contains several cells connected in series inside a single package.
Q33. The ammeter used in Activity 3.2 has a range of
The ammeter used in Activity 3.2 typically has a range of 0–1 A (or sometimes 0–2 A). This range is suitable for measuring the small currents (usually less than 1 ampere) that flow in the circuit with a few cells and a bulb. The ammeter should have an appropriate range to get accurate readings without damage.
Q34. The symbol for ohm is
The symbol for ohm (the SI unit of resistance) is Ω (Greek letter omega). It was chosen because omega is the last letter of the Greek alphabet, symbolizing the end or completion. The ohm is used to measure electrical resistance. For example, a resistance of 10 ohms is written as 10 Ω.
Q35. Chemical action inside a cell produces
Chemical action inside a cell produces a potential difference (voltage) between its terminals. The chemical reactions within the cell create a separation of charges, resulting in a potential difference. This potential difference is what drives current through an external circuit. The cell does not produce current directly—it produces potential difference, which causes current to flow when the circuit is closed.
Q36. If V = 1 V and I = 1 A, resistance is
Using Ohm’s law, R = V/I = 1 V / 1 A = 1 Ω. This is the definition of the ohm—the resistance of a conductor when a potential difference of 1 volt produces a current of 1 ampere. A resistance of 1 ohm is relatively small; typical resistors have values of ohms, kilo-ohms (kΩ), or mega-ohms (MΩ).
Q37. A device used to change resistance in a circuit is
A device used to change resistance in a circuit is a rheostat (or variable resistor). It consists of a wire coil with a sliding contact. By moving the contact, the length of wire in the circuit changes, which changes the resistance. Rheostats are used to control current in circuits, such as in dimmer switches and volume controls.
Q38. Electric pressure along a conductor is called
Electric pressure along a conductor is called potential difference (or voltage). Just as water pressure causes water to flow, potential difference causes electric charges to flow. It is the work done per unit charge to move a charge between two points. Potential difference is measured in volts (V).
Q39. 1 volt can also be written as
1 volt can be written as 1 JC⁻¹ (1 joule per coulomb). Since V = W/Q, the unit of potential difference is J/C. This can also be written as JC⁻¹. This shows that a volt is the potential difference when 1 joule of work is done to move 1 coulomb of charge.
Q40. The slope of V–I graph represents
The slope of a V–I graph represents resistance. Since V = IR, the graph is a straight line with slope ΔV/ΔI = R. A steeper slope means higher resistance, and a gentler slope means lower resistance. The V–I graph is a powerful way to determine the resistance of a conductor.
Q41. The SI unit of potential difference is
The SI unit of potential difference is the volt (V). It is named after the Italian physicist Alessandro Volta. One volt is the potential difference when 1 joule of work is done to move 1 coulomb of charge. The volt is a derived SI unit.
Q42. A schematic diagram uses
A schematic diagram uses conventional symbols to represent the components of a circuit. These symbols are standardized and universally recognised. For example, a cell is represented by a long and a short parallel line, a bulb by a circle with a cross, and a resistor by a zig-zag line. This makes circuit diagrams easy to draw and understand.
Q43. A rheostat is a type of
A rheostat is a type of variable resistance. It allows the user to change the resistance in the circuit by moving a sliding contact along a wire coil. This changes the length of wire in the circuit, thereby changing the resistance. Rheostats are commonly used in experiments to vary current and voltage.
Q44. Resistance depends on
Resistance depends on the material of the conductor (its resistivity) and temperature. Different materials have different resistivities—copper has low resistance, while nichrome has high resistance. Resistance also increases with temperature for most metals. It does not depend on the battery or the colour of the wire.
Q45. Ohm’s law was proposed in the year
Ohm’s law was proposed by Georg Simon Ohm in 1827. He published his findings in a book called “The Galvanic Circuit Investigated Mathematically.” Ohm discovered that the current through a conductor is directly proportional to the potential difference applied across it, provided the temperature remains constant.
Q46. Current is inversely proportional to
According to Ohm’s law, current (I) is inversely proportional to resistance (R) when the voltage (V) is constant. I = V/R. This means that if the resistance increases, the current decreases, and vice versa. This is why adding more resistance in a circuit reduces the current flow.
Q47. A cell can have potential difference even when
A cell can have a potential difference even when no current is drawn from it (open circuit). This is called the electromotive force (EMF) of the cell. The potential difference exists between the terminals due to the chemical reactions inside the cell, even when the circuit is open. When current flows, the terminal voltage may be slightly lower due to internal resistance.
Q48. Energy given to 1 C charge by a 6 V battery is
Energy (or work done) W = V × Q = 6 V × 1 C = 6 J. A 6 V battery gives 6 joules of energy to every coulomb of charge that flows through it. This energy is converted into other forms (like light, heat, or mechanical energy) in the circuit.
Q49. If resistance is doubled, current becomes
If resistance is doubled, the current becomes half (assuming the voltage remains constant). From Ohm’s law, I = V/R. If R is doubled, I = V/(2R) = ½ × (V/R). So the current becomes half of its original value. This shows the inverse relationship between current and resistance.
Q50. When a cell is connected to a circuit, potential difference
When a cell is connected to a circuit, the potential difference across its terminals sets charges (electrons) in motion. This motion of charges constitutes electric current. The potential difference provides the electrical pressure that drives the electrons around the circuit. Without potential difference, charges would not flow.