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Q1. The bulb in a circuit glows due to
The bulb in a circuit glows due to the heating effect of electric current. When current flows through the filament of the bulb, it heats up to a very high temperature (about 2500°C) and starts glowing. This is because the filament has high resistance, which converts electrical energy into heat and light energy.
Q2. One ampere is equal to
One ampere is defined as the flow of one coulomb of charge per second. So, 1 A = 1 C/s. This is the SI unit of electric current. The ampere is named after the French physicist André-Marie Ampère, who made significant contributions to the study of electromagnetism.
Q3. A typical electric circuit consists of
A typical electric circuit consists of a source of electricity (cell or battery), a load (bulb or resistor), connecting wires, a switch to make or break the circuit, and sometimes measuring instruments like an ammeter. All these components are connected in a closed loop for current to flow.
Q4. Milliampere (mA) is equal to
Milliampere (mA) is equal to 10⁻³ A (one-thousandth of an ampere). This unit is commonly used for small currents, such as in electronic circuits. 1 mA = 0.001 A. Similarly, microampere (µA) = 10⁻⁶ A.
Q5. The formula for electric current is
The formula for electric current is I = Q / t, where I is the current, Q is the charge flowing, and t is the time taken. This means current is the rate of flow of electric charge. If more charge flows in less time, the current is larger. The SI unit of current is ampere (A).
Q6. Electric current is a
Electric current is a scalar quantity because it has magnitude but no direction. Although current flows in a particular direction, it does not follow the rules of vector addition. When currents meet at a junction, they add algebraically (like scalars), not vectorially.
Q7. The flow of charges in metals is mainly due to
The flow of charges in metals is mainly due to free electrons. In metallic conductors, the atoms are arranged in a lattice, and the outermost electrons are loosely bound. These electrons are free to move within the metal and are called free electrons or conduction electrons. They carry electric current when a potential difference is applied.
Q8. The direction of current shown in circuit diagrams is
The direction of current shown in circuit diagrams is conventional current direction, which is from the positive terminal to the negative terminal of the battery. This convention was established before electrons were discovered. Actually, electrons flow from negative to positive (opposite to conventional current).
Q9. Ampere is named after
Ampere is named after André-Marie Ampère (1775–1836), a French physicist and mathematician. He made important contributions to the study of electromagnetism and is considered one of the founders of electrodynamics. The SI unit of electric current was named in his honour.
Q10. When a circuit is broken, the bulb
When a circuit is broken (open circuit), the bulb does not glow because the path for current flow is interrupted. Current cannot flow through a broken circuit, so the bulb receives no electrical energy and does not emit light. A switch is used to intentionally break or complete a circuit.
Q11. The function of a switch in a circuit is to
The function of a switch in a circuit is to make (close) or break (open) the circuit. When the switch is closed, the circuit is complete and current flows. When the switch is open, the circuit is broken and current stops flowing. This allows us to control electrical devices easily.
Q12. Conventionally, the direction of electric current is taken as
Conventionally, the direction of electric current is taken as opposite to the flow of electrons. This means current flows from the positive terminal to the negative terminal of a battery, while electrons actually flow from negative to positive. This convention was established before electrons were discovered.
Q13. Microampere (µA) is equal to
Microampere (µA) is equal to 10⁻⁶ A (one-millionth of an ampere). This unit is used for very small currents, such as in sensitive electronic circuits, sensors, and medical devices. 1 µA = 0.000001 A. Milliampere (mA) = 10⁻³ A.
Q14. Electric current in a circuit flows from
Electric current in a circuit flows from the positive terminal to the negative terminal of the battery (conventional current direction). Actually, electrons flow from negative to positive, but the conventional current direction is from positive to negative. This convention is used worldwide in circuit diagrams.
Q15. Electricity is considered an important form of energy because it is
Electricity is considered an important form of energy because it is convenient and controllable. It can be easily transmitted over long distances, converted into other forms of energy (light, heat, motion), and controlled with switches. It powers homes, schools, hospitals, and industries, making modern life possible.
Q16. The charge of one electron is
The charge of one electron is –1.6 × 10⁻¹⁹ C (coulombs). This is the smallest known charge and is called the elementary charge. The charge of a proton is equal in magnitude but opposite in sign: +1.6 × 10⁻¹⁹ C. This fundamental charge was first measured by Robert Millikan in his oil drop experiment.
Q17. Electric current in a conductor is due to the flow of
Electric current in a conductor is due to the flow of electric charges (electrons). In metals, the charges that flow are electrons. In liquids and gases, both positive and negative ions may carry current. Electric current is defined as the rate of flow of electric charge.
Q18. In metallic wires, electric current is due to the flow of
In metallic wires, electric current is due to the flow of electrons. Metals have free electrons (conduction electrons) that are loosely bound to their atoms. When a potential difference is applied, these electrons drift through the wire, creating an electric current. Protons and neutrons do not flow in metals.
Q19. A current of 0.5 A flows for 10 minutes. The charge flowing is
Using the formula I = Q / t, we have Q = I × t. Here, I = 0.5 A and t = 10 minutes = 10 × 60 = 600 seconds. So, Q = 0.5 × 600 = 300 C. The charge flowing is 300 coulombs. This shows how current and time determine the total charge transferred.
Q20. Electric current depends on
Electric current depends on both charge (Q) and time (t), as given by the formula I = Q / t. Current is the rate of flow of charge. A larger charge flowing in the same time gives a larger current. A smaller time for the same charge also gives a larger current.
Q21. Electric current stops flowing when
Electric current stops flowing when the circuit is broken (open circuit). A break in the circuit interrupts the path for current flow. This is the principle behind switches—when the switch is off, the circuit is broken and current stops. When the circuit is complete, current flows.
Q22. In a torch, electric current is provided by
In a torch, electric current is provided by cells or a battery. The cells convert chemical energy into electrical energy, providing a potential difference that drives current through the circuit. The bulb converts this electrical energy into light, and the switch controls the flow.
Q23. Electric current flows through a conductor when
Electric current flows through a conductor when charges flow (move) through it. Electric current is defined as the rate of flow of electric charge. If charges are stationary, there is no current. A potential difference (voltage) causes the charges to flow and create current.
Q24. An electric bulb lights up immediately because
An electric bulb lights up immediately because the electric signal propagates through the wire at nearly the speed of light (about 3 × 10⁸ m/s). This is due to the electric field, not the electrons themselves moving at that speed. Electrons actually move slowly (drift speed), but the effect is transmitted rapidly.
Q25. Electricity is widely used in
Electricity is widely used in homes, schools, hospitals, industries, and almost every aspect of modern life. It powers lighting, heating, cooling, communication, medical equipment, transportation, and manufacturing. This widespread use makes electricity one of the most important forms of energy in the modern world.
Q26. A torch bulb glows only when
A torch bulb glows only when the switch is on. When the switch is on, the circuit is complete (closed), and current flows through the bulb. When the switch is off, the circuit is broken (open), and current does not flow. A complete circuit is necessary for the bulb to glow.
Q27. Metals conduct electricity because
Metals conduct electricity because electrons can move easily through them. The free electrons (conduction electrons) in metals are not bound to any particular atom and can drift through the metal lattice when a potential difference is applied. This movement of electrons constitutes electric current.
Q28. Electric current is defined as
Electric current is defined as the rate of flow of electric charge. Mathematically, I = Q / t. It is the amount of charge passing through a cross-section of a conductor per unit time. The SI unit of electric current is the ampere (A).
Q29. Similarly, flow of charges requires
The flow of charges requires a potential difference (voltage) between two points. Just as water flows from a higher level to a lower level due to a pressure difference, charges flow from a higher potential to a lower potential. A potential difference is provided by a battery or cell.
Q30. The study of electricity in this chapter mainly explains
The study of electricity in this chapter mainly explains the flow of charges and circuits. It covers concepts like electric current, potential difference, resistance, and Ohm’s law, as well as the working of electric circuits and how electrical devices function. The focus is on basic electrical concepts and circuit analysis.
Q31. The flow of water in a pipe requires
The flow of water in a pipe requires a pressure difference between the two ends. Water flows from a region of high pressure to a region of low pressure. This is similar to how electric current requires a potential difference (voltage) to flow. The analogy helps in understanding electric circuits.
Q32. A continuous and closed path of electric current is called
A continuous and closed path of electric current is called an electric circuit. For current to flow, the circuit must be closed (no breaks). The circuit typically includes a source (battery), connecting wires, a load (bulb or resistor), and a switch to control the flow of current.
Q33. The schematic diagram of a circuit shows
The schematic diagram of a circuit shows a symbolic representation of the components. Standard symbols are used for batteries, bulbs, resistors, switches, and ammeters. This makes it easier to draw and understand circuits without showing the actual physical appearance of the components.
Q34. Electric current is measured in
Electric current is measured in amperes (A). The ampere is the SI unit of electric current. One ampere is defined as the flow of one coulomb of charge per second. Volt is the unit of potential difference, joule is the unit of energy, and coulomb is the unit of charge.
Q35. Drift speed of electrons is
The drift speed of electrons in a conductor is very slow—typically about 1 mm per second. This is much slower than the speed of light. Although electrons move slowly, the electric signal (current) propagates at nearly the speed of light because the electric field travels rapidly through the wire.
Q36. Initially, electric current was assumed to be the flow of
Initially, electric current was assumed to be the flow of positive charges (conventional current). This convention was established before electrons were discovered. Scientists believed that current flowed from the positive terminal to the negative terminal. Later, it was discovered that electrons flow in the opposite direction.
Q37. Electric current is measured using an instrument called
Electric current is measured using an instrument called an ammeter. An ammeter is always connected in series with the circuit so that the entire current flows through it. It has very low resistance to avoid affecting the current. The ammeter is used to measure the rate of flow of charge in a circuit.
Q38. The heating effect of current is discussed in
The heating effect of current is discussed in Chapter 4 of the Class 10 Physics textbook. It covers topics like the heating effect of electric current, Joule’s law of heating, and applications such as electric heaters, fuses, and bulbs. The formula H = I²Rt is a key concept in this chapter.
Q39. The SI unit of electric current is
The SI unit of electric current is the ampere (A). It is named after the French physicist André-Marie Ampère. One ampere is the amount of current when one coulomb of charge passes through a point in one second. The ampere is one of the seven base SI units.
Q40. Charges do not flow in a wire by themselves because
Charges do not flow in a wire by themselves because they need a potential difference (voltage) to move. Without a potential difference, the charges move randomly and there is no net flow of current. A battery or cell provides the potential difference that drives charges through the circuit.
Q41. The SI unit of electric charge is
The SI unit of electric charge is the coulomb (C). One coulomb is defined as the amount of charge transported by a current of one ampere in one second. It is a derived SI unit named after the French physicist Charles-Augustin de Coulomb, who studied the force between electric charges.
Q42. Flowing water in a river is an example of
Flowing water in a river is an example of water current, which is used as an analogy for electric current. Just as water current is the flow of water from a higher level to a lower level, electric current is the flow of electric charge from a higher potential to a lower potential.
Q43. If a charge Q flows in time t, the current I is given by
If a charge Q flows in time t, the current I is given by I = Q / t. This is the fundamental formula for electric current. It shows that current is the rate of flow of electric charge. If more charge flows in less time, the current is larger. The SI unit of current is ampere (A).
Q44. Electric potential difference causes
Electric potential difference causes the movement of charges (electric current). Just as a water pressure difference causes water to flow, a potential difference causes electric charges to move. This movement of charges is what we call electric current. The potential difference is provided by a battery or cell.
Q45. The average speed of electrons in a conductor is called
The average speed of electrons in a conductor is called drift speed. It is the very slow speed (about 1 mm/s) at which electrons move through the conductor when an electric field is applied. Despite this slow speed, the electric signal travels rapidly because the electric field propagates at nearly the speed of light.
Q46. Ten minutes is equal to
Ten minutes is equal to 600 seconds. Since 1 minute = 60 seconds, 10 minutes = 10 × 60 = 600 seconds. This conversion is important in physics problems involving current (I = Q / t) where time is measured in seconds. Many calculations require converting minutes to seconds.
Q47. Horizontal water in a tube does not flow because of
Horizontal water in a tube does not flow because there is no pressure difference between the two ends. Water flows from a region of high pressure to low pressure. Similarly, electric charges do not flow without a potential difference. This analogy helps in understanding why a potential difference is needed for current flow.
Q48. One coulomb of charge is approximately equal to the charge of
One coulomb of charge is approximately equal to the charge of 6 × 10¹⁸ electrons. Since the charge of one electron is 1.6 × 10⁻¹⁹ C, the number of electrons in 1 C is 1 / (1.6 × 10⁻¹⁹) = 6.25 × 10¹⁸ electrons. This large number shows how many electrons are needed to make one coulomb of charge.
Q49. An ammeter is always connected in
An ammeter is always connected in series with the circuit. This allows the entire current to pass through the ammeter. Since it measures the current flowing in the circuit, it must be placed in the path of the current. Ammeters have very low resistance so they do not affect the current in the circuit.
Q50. Gravity plays what role in the flow of electrons in a wire?
Gravity plays no role in the flow of electrons in a wire. The flow of electrons is due to the electric field and potential difference, not due to gravity. Electrons are very light and are not significantly affected by gravity. The movement of electrons is governed by electrical forces, not gravitational forces.