Std 10th Science Part 1 – Chapter 4 : Effects of Electric Current Exercise Questions And Answers Maharashtra Board

Q1. Tell the odd one out. Give proper explanation.

a. Fuse wire, bad conductor, rubber gloves, generator.

• Odd one out: Generator.
• Explanation: Fuse wire, bad conductor, and rubber gloves are related to safety and preventing the flow of electricity (insulation/circuit breaking). A generator is a device that
  produces electricity.

b. Voltmeter, Ammeter, galvanometer, thermometer.

• Odd one out: Thermometer.
• Explanation: Voltmeter, Ammeter, and Galvanometer are all instruments used for electrical measurements (potential difference, current, etc.). A thermometer measures
  temperature.

c. Loud speaker, microphone, electric motor, magnet.

• Odd one out: Magnet.
• Explanation: Loudspeaker, microphone, and electric motor are devices that use the magnetic effects of electric current (or vice versa) for their functioning, involving the conversion of energy. A magnet is a component, not a device converting energy.

Q2. Explain the construction and working of the following. Draw a neat diagram and label it.

a. Electric motor 

Construction: 

An electric motor consists of a rectangular loop of copper wire (armature) placed between the poles of a magnet. The ends of the loop are connected to two halves of a split ring (commutator). The outer surfaces of the split ring halves are in contact with two stationary carbon brushes.

Working: 

When current flows through the loop, a force is exerted on its sides (AB and CD) according to Fleming’s Left Hand Rule. Since the current direction in AB is opposite to that in CD, the forces act in opposite directions (one up, one down). This causes the loop and the axle to rotate. After every half rotation, the split ring reverses the direction of the current in the loop, ensuring the force continues to rotate the loop in the same direction. This converts electrical energy into mechanical energy.

b. Electric Generator(AC)

Construction: 

An AC generator consists of a copper wire coil (armature) placed between the poles of a magnet. The two ends of the coil are connected to two separate conducting rings (R1​ and R2​). These rings are fixed to the axle and touch stationary carbon brushes (B1​ and B2​) which are connected to the external circuit (e.g., a galvanometer).

Working: 

The axle is rotated, causing the coil to rotate in the magnetic field (mechanical energy). According to Faraday’s law of induction and Fleming’s Right Hand Rule, an induced current is produced in the coil. In the first half-rotation, the current flows in one direction ( B2​ to B1​ in the external circuit). In the next half-rotation, the current’s direction is reversed (B1​ to B2​). This produces alternating current (AC), which changes direction after every half-rotation.

Q3. Electromagnetic induction means-

a. Charging of an electric conductor.

b. Production of magnetic field due to a current flowing through a coil.

c. Generation of a current in a coil due to relative motion between the coil and the magnet.

d. Motion of the coil around the axle in an electric motor.

Answer – c. Generation of a current in a coil due to relative motion between the coil and the magnet.

Q4. Explain the difference : AC generator and DC generator.

Feature	AC Generator	DC Generator
Current Produced	Alternating Current (AC)	Direct Current (DC)
Current Direction	Changes direction in the external circuit after every half rotation.	Flows in only one direction in the external circuit.
Connection to Coil	Two separate conducting rings (Slip Rings).	Split ring (commutator) fixed on the axle, like in an electric motor.
Principle	Electromagnetic Induction.	Electromagnetic Induction.

Q5. Which device is used to produce electricity? Describe with a neat diagram. 

a. Electric motor 

b. Galvanometer 

c. Electric Generator (DC) 

d. Voltmeter 

Answer – Device:Electric Generator(DC)

The device used to produce electricity among the given options is the Electric Generator (Option c).

Electric Generator (DC)

An Electric Generator converts mechanical energy into electrical energy based on the principle of electromagnetic induction.

Principle

When a conducting coil is rotated in a magnetic field, the number of magnetic lines of force passing through the coil changes, and an induced current is produced in the coil. The direction of this current is given by Fleming’s Right Hand Rule.

Construction

• Armature Coil (ABCD): A conducting wire coil that rotates in the magnetic field.
• Magnet: Provides the strong magnetic field.
• Split Ring (Commutator): The two ends of the coil are connected to the two halves (R1​ and R2​) of a split ring fixed on the axle.
• Carbon Brushes (B1​ and B2​): Two stationary brushes maintain contact with the rotating split ring halves and are connected to the external circuit.

Working (Producing DC Current)

1. Rotation: The coil is rotated around the axle, often by an external machine (mechanical energy).
2. Current Induction: As the coil rotates, an electric current is induced in the coil.
3. DC Output: The split ring (commutator) ensures that the coil branch going upwards is always in contact with one brush (B1​) and the branch going downwards is always in contact with the other brush (B2​).

Result: This arrangement reverses the connection to the external circuit every half-rotation, ensuring the induced current flows in one direction only in the external circuit, producing Direct Current (DC).

Q6. How does the short circuit form? What is its effect?

Answer – 

Formation (Short Circuit): A short circuit occurs when the live wire and the neutral wire in a home electrical connection come into contact with each other. This happens due to a fault in the equipment or when the plastic coating on the wires wears off.

Effect:

• A very large current flows through the circuit.
• This current produces a large amount of heat.
• If any flammable material is nearby, it can catch fire.

A fuse wire is used as a safety measure: it melts and breaks the circuit when high current flows, preventing a mishap.

Q7. Give Scientific reasons.

a. Tungsten metal is used to make a solenoid type coil in an electric bulb.

• Reason: Tungsten wire is used because it has a very high melting point (nearly 3400∘C). Due to the heating effect of the current, the tungsten coil gets heated to a very high temperature and emits light. Its high melting point prevents it from melting.

b. In the electric equipment producing heat e.g. iron, electric heater, boiler, toaster etc. an alloy such as Nichrome is used, not pure metals.

• Reason: Nichrome is an alloy with a higher resistivity than pure metals. According to Joule’s law of heating (H=I2×R×t), a high resistance (R) produces a large amount of heat, making it efficient for heating equipment. Also, alloys generally have high melting points and do not oxidize easily at high temperatures.

c. For electric power transmission, copper or aluminium wire is used.

• Reason: Copper and Aluminium are excellent conductors of electricity, meaning they have very low resistivity. Using materials with low resistance minimizes the amount of electrical energy wasted as heat during the transmission of power over long distances.

d. In practice the unit kWh is used for the measurement of electrical energy, rather than joule.

• Reason: The Joule (J) is a very small unit of electrical energy. For practical use, especially when measuring consumption over a long period (like a month), the kilowatt-hour (kWh) is used because it is a much larger and more convenient unit. 
• (1 kWh=3.6×106 J) .

Q8. Which of the statement given below correctly describes the magnetic field near a long, straight current carrying conductor? 

a. The magnetic lines of force are in a plane, perpendicular to the conductor in the form of straight lines. 

b. The magnetic lines of force are parallel to the conductor on all the sides of conductor. 

c. The magnetic lines of force are perpendicular to the conductor going radially outward. 

d. The magnetic lines of force are in concentric circles with the wire as the center, in a plane perpendicular to the conductor.

Answer – 

Correct Option: d. The magnetic lines of force are in concentric circles with the wire as the center, in a plane perpendicular to the conductor.

Q9. What is a solenoid? Compare the magnetic field produced by a solenoid with the magnetic field of a bar magnet. Draw neat figures and name various components.

Answer – 
Solenoid: When a copper wire with a resistive coating is wound in a chain of loops (like a spring), it is called a solenoid.

Comparison:

• When an electric current passes through a solenoid, the
  magnetic field pattern it produces is very similar to the magnetic field produced by a bar magnet.

• A current-carrying solenoid acts like a bar magnet: one open end acts as the magnetic North pole, and the other acts as the magnetic South pole.
• The magnetic field inside the solenoid is uniform everywhere (lines of force are parallel to each other).

Q10. Name the following diagrams and explain the concept behind them.

Answer –

Diagram a : Fleming’s Right Hand Rule

• Name: Fleming’s Right Hand Rule.
• Concept: This rule is used to find the direction of the induced current produced when a conductor is moved in a magnetic field. This phenomenon is called Electromagnetic Induction and is the basis for an Electric Generator.

• The Rule: If you stretch the thumb, index finger, and middle finger of your right hand so they are perpendicular to each other:
  • The Thumb indicates the direction of the Motion of the Conductor.
  • The Index Finger indicates the direction of the Magnetic Field.
  • The Middle Finger shows the direction of the Induced Current.

Diagram b : Fleming’s Left Hand Rule

• Name: Fleming’s Left Hand Rule.
• Concept: This rule is used to find the direction of the force (or motion) exerted on a current-carrying conductor when it is placed in a magnetic field. It is the fundamental principle behind an Electric Motor.

• The Rule: If you stretch the thumb, index finger, and middle finger of your left hand so they are perpendicular to each other:
  • The Index Finger points in the direction of the Magnetic Field.
  • The Middle Finger points in the direction of the Current.

The Thumb points in the direction of the Force acting on the conductor.

Q11. Identify the figures and explain their use.

Answer – 

a. (Image of Fuses)

• Identification: Different types of Fuses (e.g., cartridge fuses, kit-kat fuses).
• Use: A fuse contains a thin wire with a low melting point. It is used as a precautionary measure in a circuit. When the current suddenly becomes too high (due to short circuiting or overloading), the fuse wire melts,breaks the circuit, and protects the appliances and wiring from damage or fire.

b. (Image of Miniature Circuit Breakers – MCBs)

• Identification: Miniature Circuit Breakers (MCBs).
• Use: These switches are used in homes instead of traditional fuses. When the current in the circuit suddenly increases beyond a safe limit, this switch automatically
  opens (trips), stopping the flow of current and preventing mishaps.

c. (Image of Electric Generator (DC))

Here, an ammeter is shown instead of a bulb.

Electric Generator (DC)

• Identification: The figure represents the basic Electric Generator setup, specifically for Direct Current (DC) output, as indicated by the split ring (commutator) on the axle.
• Use (Function): An Electric Generator is a device used to produce electricity by converting mechanical energy into electrical energy.Explanation (Working Principle)

The DC generator works on the principle of electromagnetic induction:

1. Induction: The external circuit (not fully shown) provides mechanical energy to rotate the armature coil (the rectangle) between the magnetic poles.
2. Current Generation: As the coil rotates, the number of magnetic lines of force passing through it changes, inducing a current in the coil.
3. DC Output: The induced current in the coil is alternating, but the split ring (commutator) ensures that the current flowing through the external circuit (which includes the ammeter ‘A’) remains unidirectional, thereby producing Direct Current (DC)

Q12. Solve the following example. 

a. Heat energy is being produced in a resistance in a circuit at the rate of 100 W. The current of 3 A is flowing in the circuit. What must be the value of the resistance?(Ans : 11 W)

Answer – 

Given: 

Power (P) = 100 W (rate of heat production), Current (I) = 3 A.

Formula (Joule’s Law of Heating in terms of Power) : P=I²×R.

Calculation:
100 W=(3A)²×R
100=9×R
R =100​ / 9 ≈ 11.11 Ω

Answer: The value of the resistance is approximately 11 Ω (As per the textbook answer: 11 Ω).

b. Two tungsten bulbs of wattage 100 W and 60 W power work on 220 V potential difference. If they are connected in parallel, how much current will flow in the main conductor?

Answer – 

Given: Potential Difference (V) = 220 V. 

Bulb 1 Power (P₁​) = 100 W. 

Bulb 2 Power (P₂​) = 60 W.

Concept: In a parallel circuit, the total power consumed is the sum of the individual powers: P_total​=P₁​+P₂​. Total current (Itotal​) is found using P_total​ = V × I_total​.

Calculation:
P_total​= 100 W + 60 W = 160 W
I_total​ = P_total​​ / V = 160 W​ / 220 V ≈ 0.727 A
Answer: The total current that will flow in the main conductor is approximately 0.72 A.

c. Who will spend more electrical energy? 500 W TV Set in 30 mins, or 600 W heater in 20 mins?

Answer – 

Concept: Energy (E) = Power (P) × Time (t). Time must be in a consistent unit (hours or seconds). Let’s use minutes for comparison.

TV Set:
E_TV​ = 500 W × 30 mins = 15000 W-min

Heater:
E_Heater​=600 W × 20 mins = 12000 W-min

Comparison: 15000 W-min > 12000 W-min.

Answer: The TV Set will spend more electrical energy.

d. An electric iron of 1100 W is operated for 2 hrs daily. What will be the electrical consumption expenses for that in the month of April? (The electric company charges Rs 5 per unit of energy).

Answer – 

Given: Power (P) = 1100 W=1.1 kW (since 1 unit=1 kWh). 

Daily Time (t) = 2 hrs. 

No. of days in April = 30 days. 

Cost per unit = Rs 5.

Calculation:
Daily Consumption = P × t = 1.1 kW × 2 hrs = 2.2 kWh/day
Monthly Consumption= 2.2 kWh/day × 30 days = 66 kWh
Total Expense = 66 units × Rs 5/unit = Rs 330

Answer: The electrical consumption expenses for April will be Rs 330.