Class 10 Science Chapter 11 Question Answers - Electricity

Q1: Explain the concept of electric current and its flow in a closed circuit. Describe the role of electric charges in the formation of an electric current.
Ans: Electric current is the flow of electric charges through a conductor. It occurs when there is a potential difference (voltage) across a closed circuit. The flow of electric charges is driven by the presence of free electrons within the conductor.
Formation of Electric Current:

• Electric charges, specifically electrons, are present within the atoms of a conductor. In metals, some electrons are loosely bound and can move freely.
• When a potential difference is applied across the ends of a conductor, it creates an electric field that exerts a force on the free electrons.
• The electrons start to drift in response to this force, creating a flow of charges in one direction. This flow of charges constitutes an electric current.

Role of Electric Charges:

• The movement of electric charges, mainly electrons, within the conductor is responsible for the creation of an electric current.
• The transfer of electrons from atom to atom results in the flow of charges, leading to the conduction of electricity through the material.

Q2: Explain Ohm's law and its mathematical representation. Describe the relationship between voltage, current, and resistance in an electrical circuit.
Ans: Ohm's law states that the current passing through a conductor is directly proportional to the voltage applied across it, provided its temperature remains constant. Mathematically, Ohm's law is represented as:
V = I . R
Where:

• V is the voltage (potential difference) across the conductor in volts (V).
• I is the current flowing through the conductor in amperes (A).
• R is the resistance of the conductor in ohms (Ω).

Relationship between Voltage, Current, and Resistance:

• According to Ohm's law, the current (I) flowing through a conductor is directly proportional to the voltage (V) applied across it. In other words, as the voltage increases, the current also increases, assuming the resistance remains constant.
• Resistance (R) is a measure of how much a conductor opposes the flow of current. It is inversely proportional to the current: higher resistance leads to lower current, and vice versa.

Ohm's law provides a fundamental relationship in electricity and helps in understanding how changes in voltage, current, and resistance affect each other in an electrical circuit.

Q3: Describe the construction and working of an electric circuit with the help of a schematic diagram. Explain the role of a switch, connecting wires, and components such as resistors in the circuit.
Ans: An electric circuit is a closed pathway through which electric current flows. It consists of various components interconnected by conductive wires. Let's consider a simple circuit with a switch, a resistor, and a power source (battery).
The construction and working of the circuit are as follows:

• Components: The circuit includes a power source (battery), a resistor, a switch, and connecting wires.
• Schematic Diagram: A schematic diagram represents the circuit using symbols. The battery is represented by a long line with a shorter line, indicating the positive and negative terminals. The resistor is represented by a zigzag line, and the switch is represented by an open or closed line.
• Switch: The switch controls the flow of current in 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 cannot flow.
• Connecting Wires: Conductive wires connect the components in the circuit, allowing the flow of electric current. They provide a pathway for the electrons to move from the negative terminal of the battery to the positive terminal.
• Resistor: The resistor offers resistance to the flow of electric current. It helps regulate the current in the circuit. As current flows through the resistor, it encounters resistance, causing a potential difference (voltage drop) across the resistor.

Role of Components:

• Power Source: Provides the potential difference (voltage) to drive the current in the circuit.
• Switch: Controls the circuit's on/off state, allowing or blocking the flow of current.
• Connecting Wires: Carry the current between components and maintain the circuit's continuity.
• Resistor: Regulates the current by converting some of the electrical energy into heat.

In summary, an electric circuit consists of interconnected components and conductive wires, with the flow of electric current controlled by switches. Components like resistors introduce resistance and regulate current flow in the circuit.

Q4: Describe the concept of electric potential difference (voltage) in an electric circuit. Explain how the voltage across a resistor affects the current flowing through it.
Ans: Electric potential difference, also known as voltage, is the driving force that pushes electric charges to move in a circuit. It represents the energy transferred per unit charge as charges flow from a higher potential to a lower potential. Voltage is measured in volts (V).
Effect of Voltage on Current through a Resistor:

• According to Ohm's law (V = I ⋅ R), the current (I) flowing through a resistor is directly proportional to the voltage (V) across it, assuming the resistance (R) remains constant.
• Higher voltage leads to an increased potential difference across the resistor, resulting in an increased current.
• Lower voltage causes a decreased potential difference and, consequently, a reduced current through the resistor.
• The relationship between voltage and current through a resistor is linear, provided the resistor's temperature and other conditions remain constant.

Q5: Explain the term "electric power" in an electrical circuit. Describe the relationship between electric power, current, and voltage. Provide the mathematical formula for calculating electric power.
Ans: Electric power is the rate at which electric energy is converted into other forms of energy, such as heat, light, or mechanical work, in an electrical circuit. It is measured in watts (W).
Relationship between Electric Power, Current, and Voltage:

• Electric power (P) is directly proportional to the product of current (I) and voltage (V) across a component. Mathematically, this relationship is expressed as:
  P = I ⋅ V
• The unit of electric power is the watt (W), which is equal to one joule per second (1 J/s).
• The formula indicates that higher currents or voltages result in increased electric power. Power consumption is higher when a component operates at a higher current and/or voltage.

Q6: Describe the working principle of an electric fuse and its role in electrical safety. Explain how a fuse prevents excessive current flow in a circuit.
Ans: An electric fuse is a safety device designed to protect electrical circuits and appliances from damage due to excessive current flow. It contains a thin wire that melts when subjected to high current, breaking the circuit and stopping the flow of electricity.
Working Principle and Role in Electrical Safety:

• The fuse is connected in series with the circuit. When the current passing through the circuit exceeds the rated current of the fuse, the fuse wire heats up due to increased resistance.
• The heat generated by the excessive current causes the fuse wire to melt, creating an open circuit and interrupting the flow of electricity.
• By breaking the circuit, the fuse prevents further current from flowing, protecting the circuit and connected devices from damage.

Importance of Fuses in Electrical Safety:

• Fuses play a crucial role in preventing electrical fires and protecting equipment from damage caused by overcurrent.
• They offer a sacrificial element that breaks under excessive current, diverting the current away from sensitive components.

Q7: Explain the concept of electric resistance and its factors. Describe how the length, cross-sectional area, and material of a conductor affect its resistance.
Ans: Electric resistance (R) is the opposition offered by a material to the flow of electric current. It depends on the material's properties, length (l), cross-sectional area (A) of the conductor, and temperature.

Factors Affecting Electric Resistance:

• Length (l): Resistance is directly proportional to the length of the conductor. Longer conductors offer more resistance, as electrons have to travel a greater distance, increasing the chance of collisions.
• Cross-Sectional Area (A): Resistance is inversely proportional to the cross-sectional area of the conductor. Wider conductors provide less resistance, as electrons have more space to flow, reducing the chance of collisions.
• Material: Different materials have different resistivities (ρ), a property that determines their inherent resistance. Materials with higher resistivities offer greater resistance to the flow of current.

Mathematical Relationship:
The resistance (R) of a conductor can be calculated using the formula:
R = ρ⋅l/A
Where:

• ρ is the resistivity of the material.
• l is the length of the conductor.
• A is the cross-sectional area of the conductor.

In summary, resistance depends on the length, cross-sectional area, and material of a conductor. Longer conductors with smaller cross-sectional areas and materials with higher resistivities result in greater resistance.

Q8: Explain the working of an electric bell with the help of a circuit diagram. Describe the role of the electromagnet, armature, and contact points in the operation of the electric bell.
Ans: An electric bell is a simple device that converts electrical energy into mechanical motion and sound. It operates through the interaction of an electromagnet, an armature, and contact points.
The working of an electric bell is as follows:
Working Principle:

• Circuit Closed: When the switch is closed, current flows through the circuit.
• Electromagnet: The current passes through the coil of an electromagnet, creating a magnetic field around it.
• Attraction of Armature: The magnetic field attracts the iron armature, pulling it toward the electromagnet.
• Breaking Contact: As the armature moves, it separates from the contact points (normally closed), breaking the circuit and stopping the flow of current.
• Magnetic Field Collapses: With the circuit broken, the electromagnet's magnetic field collapses, releasing the armature.
• Return Spring: A return spring attached to the armature pulls it back to its original position when the magnetic attraction is lost.
• Reconnection: As the armature moves back, it closes the contact points, completing the circuit again.
• Cycle Repeats: The cycle of attraction, breaking contact, release, and return continues as long as the switch remains closed.

Role of Components:

• Electromagnet: The coil of wire wrapped around an iron core generates a strong magnetic field when current flows through it, attracting the armature.
• Armature: The iron piece is attracted by the electromagnet's magnetic field, causing it to move and break the circuit.
• Contact Points: The points where the circuit is broken and reconnected, controlling the flow of current.

Q9: Describe the difference between direct current (DC) and alternating current (AC) in an electrical circuit. Explain the generation and distribution of AC using the example of a power station and household appliances.
Ans: Direct Current (DC) and Alternating Current (AC) are two types of electric currents with distinct characteristics.
Difference between DC and AC:

• Direct Current (DC): In DC, the flow of electric charges is unidirectional, meaning it flows in a single direction. Batteries and cells are common sources of DC.
• Alternating Current (AC): In AC, the direction of electric current reverses periodically, oscillating back and forth. AC is used for the distribution of electrical power in most households and industries.

Generation and Distribution of AC:

• Power Generation: AC is generated at power stations using generators. These generators produce AC by rotating coils of wire within a magnetic field. The changing magnetic field induces an alternating current in the coils.
• Transmission: The generated AC is transmitted at high voltages over long distances to reduce energy losses. High-voltage transmission lines carry AC power from power stations to substations.
• Step-Down Transformer: At substations, step-down transformers reduce the voltage to a safer level for distribution to households and businesses.
• Distribution: AC power is distributed through power lines to homes and industries. Electrical appliances are designed to operate on AC.
• Household Appliances: AC powers a wide range of household appliances, from lighting to heating and cooling systems. When AC voltage changes direction, it allows electric motors in appliances to operate effectively.

In summary, AC is generated, transmitted, and distributed for various applications, including powering household appliances, due to its ability to be easily transformed and transmitted over long distances with minimal energy loss.

Q10: (a) List the factors on which the resistance of a conductor depends.
(b) A 4 kW heater is connected to a 220 V source of power. Calculate
(i) the electric current passing through the heater.
(ii) the resistance of the heater.
(iii) the electric energy consumed in 2 hour use of the heater.
Ans: (a) Resistance of a conductor depends on
(i) length of conductor (l)
(ii) Area of cross-section (A)
(iii) Resistivity of material (ρ)
Relation of resistance is given by,
(b) Given, P = 4 kW = 4000 W and V = 220 V
(i) P = VI or I = P/A
Hence, I = 4000/220 = 18.18 A
(ii) V = IR or R = V/I
R = 220/18.18 = 12.1Ω
(iii) Energy consumed, E = P × t
E = 4000 W × 2h = 8000Wh = 8 kWh = 8 unit.