Class 10 Science1 Chapter 4 – Effects of Electric Current

Class 10 Science and Technology Part 1
Chapter 4 – Effects of Electric Current

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

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

Answer: Generator

Explanation: Fuse wire, bad conductor and rubber gloves are related to electrical safety and insulation, whereas a generator produces electrical energy.

b. Voltmeter, Ammeter, galvanometer, thermometer

Answer: Thermometer

Explanation: Voltmeter, ammeter and galvanometer are electrical measuring instruments, whereas a thermometer measures temperature.

c. Loud speaker, microphone, electric motor, magnet

Answer: Magnet

Explanation: Loud speaker, microphone and electric motor are electrical devices that work using the magnetic effect of electric current, whereas a magnet itself does not require electric current to produce its magnetic effect.

2. 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 coil ABCD of insulated copper wire placed between the poles of a strong permanent magnet. The coil is mounted on an axle. The two ends of the coil are connected to a split-ring commutator. Two carbon brushes press against the commutator and are connected to a battery.

Neat Labelled Diagram

Working

When electric current is passed through the coil, the two sides of the coil experience forces in opposite directions due to the magnetic field. These forces produce a turning effect and the coil starts rotating. The split-ring commutator reverses the direction of current in the coil after every half rotation, so the coil continues to rotate in the same direction.

Principle: An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force.

b. Electric Generator (AC)

Construction

An AC generator consists of a rectangular coil ABCD of insulated copper wire placed between the poles of a strong magnet. The coil is mounted on an axle. The two ends of the coil are connected to two separate conducting rings called slip rings. Carbon brushes press against the slip rings and are connected to the external circuit.

Neat Labelled Diagram

Working

When the coil is rotated mechanically in the magnetic field, the magnetic flux linked with the coil changes. Therefore, an electric current is induced in the coil. The direction of induced current changes after every half rotation of the coil. Hence, the current obtained from an AC generator is alternating current.

Principle: An electric generator works on the principle of electromagnetic induction.

3. 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.

Explanation: Electromagnetic induction is the phenomenon in which electric current is generated in a coil due to relative motion between the coil and a magnet.

4. Explain the difference: AC Generator and DC Generator.

AC Generator	DC Generator
It produces alternating current (AC).	It produces direct current (DC).
It uses slip rings.	It uses a split-ring commutator.
The direction of current changes periodically.	The direction of current remains the same.
It is commonly used for generating AC electricity.	It is used where direct current is required.

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

a. Electric motor 
b. Galvanometer
c. Electric Generator (DC) 
d. Voltmeter

Answer: (c) Electric Generator (DC)

An electric generator is a device used to produce electricity by converting mechanical energy into electrical energy.

Working: When a coil is rotated between the poles of a magnet, the magnetic flux linked with the coil changes. Due to electromagnetic induction, an electric current is induced in the coil. In a DC generator, a split-ring commutator makes the current flow in one direction through the external circuit.

Main parts: Magnet, armature (coil), split-ring commutator and brushes.

Simple Diagram of DC Generator

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

A short circuit occurs when the live wire and neutral wire come into direct contact due to damaged insulation or some other fault. This provides a path of very low resistance, causing a large current to flow.

Effects of short circuit:

1. A very large current flows through the circuit.
2. The wires may become overheated.
3. The fuse may melt or the MCB may trip.
4. Electrical appliances may get damaged.
5. It may cause a fire.

7. Give Scientific Reasons

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

Answer: Tungsten has a very high melting point and high electrical resistance. When electric current passes through the tungsten filament, it becomes white hot and emits light without melting. Therefore, tungsten is used to make the filament of an electric bulb.

b. In electric equipment producing heat, an alloy such as Nichrome is used, not pure metals.

Answer: Nichrome has high electrical resistance and a high melting point. It produces a large amount of heat when electric current passes through it and does not melt easily at high temperature. Therefore, Nichrome is used in electric heaters, irons, toasters, boilers, etc.

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

Answer: Copper and aluminium have low electrical resistance and are good conductors of electricity. Hence, very little electrical energy is lost as heat during transmission. Therefore, copper or aluminium wires are used for electric power transmission.

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

Answer: The amount of electrical energy consumed in homes and industries is very large. Measuring it in joules gives very large numerical values. Therefore, the larger and more convenient unit kilowatt-hour (kWh) is used for measuring electrical energy.

8. Which of the statements 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 the 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 around a long, straight current-carrying conductor are concentric circles, with the wire as the center, in a plane perpendicular to the conductor.

Therefore, option (d) is correct.

Q.9. 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 the various components.

Answer:

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

Magnetic field due to a solenoid: When an electric current passes through a solenoid, magnetic lines of force are produced in the pattern shown in the figure. The magnetic field of a solenoid is very similar to the magnetic field produced by a bar magnet.

Comparison with a bar magnet:

• The two open faces of a solenoid become North (N) and South (S) poles, just like a bar magnet.
• The magnetic field pattern of a current-carrying solenoid is similar to that of a bar magnet.
• The magnetic lines of force inside a long solenoid are parallel to each other.
• The magnetic field inside a long solenoid is uniform, i.e. the strength of the magnetic field is nearly the same at all points inside it.
• Outside the solenoid, the magnetic lines of force form closed curves, similar to those of a bar magnet.

Thus, a current-carrying solenoid behaves like a bar magnet.

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Q.10. Name the following diagram and explain the concept behind them.

Answer:

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(a) Fleming’s Right Hand Rule

Figure (a) represents Fleming’s Right Hand Rule. According to this rule, when the thumb, index finger and middle finger of the right hand are held mutually perpendicular to each other:

• The thumb indicates the direction of motion of the conductor.
• The index finger indicates the direction of the magnetic field.
• The middle finger indicates the direction of the induced current.

This rule is used to determine the direction of the induced current in a conductor moving in a magnetic field.

(b) Fleming’s Left Hand Rule

Figure (b) represents Fleming’s Left Hand Rule. According to this rule, when the thumb, index finger and middle finger of the left hand are held mutually perpendicular to each other:

• The index finger indicates the direction of the magnetic field.
• The middle finger indicates the direction of current.
• The thumb indicates the direction of force or motion of the conductor.

This rule is used to determine the direction of force or motion acting on a current-carrying conductor placed in a magnetic field.

Q.11. Identify the figures and explain their use.

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Answer:

(a) Electric Fuse:
This is an electric fuse. It is used to replace the fuse wire.

(b) MCB:
This is an MCB (Miniature Circuit Breaker). It is a switch used to make the current in the circuit “on or off”, i.e. to stop the current.

(c) Electric Generator:
This is an electric generator. It is used to generate electric current.

Q.12. Solve the following examples.

(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?

Given:

Heat energy produced per second, P = 100 W
Current flowing, I = 3 A

Solution:

Heat energy produced in the circuit in time t is given by:

H = Pt = VIt

∴ P = VI

Here, P = 100 W and I = 3 A

100 = V × 3

∴ V = ¹⁰⁰⁄₃ V

According to Ohm's law,

R = ^V⁄_I

R = ^100/3⁄₃

∴ R = ¹⁰⁰⁄₉ Ω

R ≈ 11 Ω

Answer: The value of resistance is approximately 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?

Given:

Power of first bulb, P₁ = 100 W
Power of second bulb, P₂ = 60 W
Potential difference, V = 220 V

Solution:

Let the currents passing through the 100 W and 60 W bulbs be I₁ and I₂, respectively.

Since the bulbs are connected in parallel, the potential difference across both bulbs is 220 V.

For the 100 W bulb:

P = VI₁

100 = 220I₁

∴ I₁ = ¹⁰⁰⁄₂₂₀ = ⁵⁄₁₁ A

For the 60 W bulb:

P = VI₂

60 = 220I₂

∴ I₂ = ⁶⁰⁄₂₂₀ = ³⁄₁₁ A

The current flowing through the main conductor is:

I = I₁ + I₂

I = ⁵⁄₁₁ + ³⁄₁₁

I = ⁸⁄₁₁ A

I ≈ 0.72 A

Answer: Current through the main conductor is 0.72 A.

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

Solution:

Electrical energy spent = Power × Time

Here, P = Power in watt and t = time in seconds.

Energy spent by TV set:

E = P × t

= 500 × 30 × 60

= 9,00,000 J

Energy spent by heater:

E = P × t

= 600 × 20 × 60

= 7,20,000 J

Since 9,00,000 J > 7,20,000 J,

Answer: The 500 W 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.

Solution:

Time for which the iron is used

= 2 × 30

= 60 hours

Power of iron = 1100 W

= ¹¹⁰⁰⁄₁₀₀₀ kW

= 1.1 kW

Energy consumed = Power × Time

= 1.1 × 60

= 66 kWh

1 kWh = 1 unit

Therefore, energy consumed = 66 units

Expense = Number of units × Rate

= 66 × Rs. 5

= Rs. 330

Answer: The electrical consumption expense for the month of April is Rs. 330.