Q1)Choose the correct option and rewrite the statement:
1. Electromagnetic induction means _______.
Answer :(c) Generating current in a coil due to relative motion between the coil and the magnet.
Electromagnetic induction means generating electric current in a closed conductor coil due to relative motion between the coil and a magnetic field.
2. To detect the presence of electric current in a circuit, which instrument is used?
Answer :(b) Galvanometer
A galvanometer is an extremely sensitive instrument used to detect both the presence and direction of minute electric currents in an electrical circuit.
3. The magnetic field lines inside a current-carrying solenoid are _______.
Answer :(a) Parallel straight lines
The magnetic field lines inside a long current-carrying solenoid are parallel straight lines, indicating that the magnetic field is uniform at all internal points.
4. Which of the following works on the principle of Fleming’s Left-Hand Rule?
Answer :(c) Electric Motor
An electric motor operates on the principle that a current-carrying conductor in an external magnetic field experiences a mechanical force, the direction of which is given by Fleming's Left-Hand Rule.
Q2)Explain the construction and working of the following:
1. Electric Motor (DC Motor)
Answer :
Principle: An electric motor converts electrical energy into mechanical energy. It works on the principle that a current-carrying coil placed in a magnetic field experiences a force that causes it to rotate continuously.
Construction:
Armature Coil (ABCD): An insulated copper wire wound on a soft iron core.
Strong Horseshoe Magnet (N-S): Creates a powerful uniform magnetic field around the coil.
Split-Ring Commutator (P and Q): A copper ring split into two halves. It reverses the direction of current in the coil after every half-rotation.
Carbon Brushes (X and Y): Fixed carbon blocks that keep contact with the rotating split rings.
DC Power Source: Supplies electric current to the coil through the brushes.
Working:
When current flows from A to B and C to D, according to Fleming's Left-Hand Rule, arm AB is pushed downward and arm CD is pushed upward.
These two opposite forces make the coil rotate in an anticlockwise direction.
After half a rotation (180°), the split rings change contact with the brushes, reversing the current direction so the coil keeps rotating in the same direction.
Fig 4.1: Schematic Diagram of an Electric Motor (DC Motor)
2. AC Generator
Answer :
Principle: An AC generator converts mechanical energy into alternating electrical energy based on Faraday's Law of Electromagnetic Induction. When an armature coil rotates in a magnetic field, the magnetic flux linked with it changes continuously, inducing an alternating current.
Construction:
Armature Coil (ABCD): Rectangular copper coil mounted on an axle between two magnetic poles.
Slip Rings (R₁ and R₂): Two complete continuous brass/copper rings that rotate with the coil.
Carbon Brushes (B₁ and B₂): Stationary brushes that rest against the slip rings to collect induced current.
Working:
When the coil is mechanically rotated clockwise, arm AB moves upward and arm CD moves downward.
By Fleming's Right-Hand Rule, induced current flows in the direction A → B → C → D.
After half a rotation (180°), arm AB moves downward and arm CD moves upward. The direction of induced current reverses, flowing as D → C → B → A.
Because current reverses direction after every half-turn, an Alternating Current (AC) is generated.
Q3)What is electromagnetic induction? Explain with the help of Faraday’s experiment.
Answer :
The phenomenon of producing an induced electromotive force (EMF) and electric current in a closed conducting circuit whenever the magnetic flux linked with the circuit changes with time is called electromagnetic induction.
Faraday's Coil and Magnet Experiment:
A sensitive galvanometer is connected across a stationary coil of insulated wire.
When the North pole of a bar magnet is thrust rapidly into the coil, the galvanometer needle deflects momentarily in one direction, demonstrating an induced current.
When the magnet is held stationary inside the coil, the galvanometer deflection drops to zero.
When the magnet is pulled out of the coil, the galvanometer deflects in the opposite direction.
Conclusion: Current is induced only during relative motion between the magnet and coil, proving that a changing magnetic flux induces current.
Q4)Explain the following rules with statements:
1. Right-Hand Thumb Rule
Answer :
Imagine that you are holding a current-carrying straight conductor in your right hand such that your stretched thumb points in the direction of the electric current. Then, the fingers curled around the conductor point in the direction of the concentric magnetic field lines.
2. Fleming’s Left-Hand Rule (For Motor)
Answer :
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of the electric current, then the thumb points in the direction of the mechanical force acting on the conductor.
3. Fleming’s Right-Hand Rule (For Generator)
Answer :
Stretch the thumb, forefinger, and middle finger of the right hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the thumb points in the direction of the motion of the conductor, then the middle finger points in the direction of the induced electric current.
Q5)Write scientific reasons:
1. Tungsten is used to make a solenoid type coil in an electric bulb.
Answer :
An incandescent electric bulb produces light by heating its filament to white incandescence (over 2500°C) through Joule heating (H = I²Rt).
Tungsten has an exceptionally high melting point (approx. 3422°C) and high electrical resistivity.
It does not melt, deform, or oxidize easily even at glowing white temperatures.
Coiling it into a fine solenoid-shaped filament concentrates heat, enhancing luminescence efficiency.
2. For electric power transmission, copper or aluminium wire is used.
Answer :
Copper and aluminium are excellent electrical conductors with very low electrical resistivities (ρ).
According to Joule’s law of heating (H = I²Rt), transmission lines with low resistance dissipate minimal electrical energy as wasted heat.
They are ductile, corrosion-resistant, and relatively lightweight, making them ideal for long-distance power grids.
3. A fuse wire is made of a material having a low melting point.
Answer :
An electric fuse is a critical safety device connected in series with the live wire.
When excessive current flows due to overloading or a short circuit, Joule heating (H = I²Rt) increases drastically.
Because the fuse wire is composed of an alloy (lead and tin) with a low melting point, it melts quickly and breaks the electrical circuit.
This halts the excessive current flow, protecting domestic appliances from burnouts and preventing electrical fires.
Q6)Distinguish between the following:
1. Alternating Current (AC) and Direct Current (DC)
Answer :
Alternating Current (AC)
Direct Current (DC)
Direction and magnitude change periodically with time.
Flows continuously in only one fixed direction.
In India, AC has a frequency of 50 Hz.
Frequency of DC is 0 Hz.
Can be stepped up or down efficiently using transformers.
Cannot be stepped up or down easily using transformers.
Can be transmitted over long distances with minimal power loss.
Transmission over long distances results in substantial power loss.
Sources: AC generators, domestic power mains.
Sources: Electrochemical cells, dry batteries, solar cells.
2. Solenoid and Bar Magnet
Answer :
Current-Carrying Solenoid
Permanent Bar Magnet
It is an electromagnet; magnetic field exists only while current flows.
It is a permanent magnet with a constant magnetic field.
Magnetic strength can be adjusted by changing current or number of turns.
Magnetic strength is fixed and cannot be easily varied.
Polarity can be reversed by changing current direction.
Magnetic poles (N and S) are fixed and cannot be reversed.
Q7)What is a solenoid? Compare the magnetic field produced by a solenoid with the magnetic field of a bar magnet.
Answer :
A long coil of wire consisting of many closely spaced helical loops of insulated copper wire wound on a cylindrical core is called a solenoid.
Comparison:
When direct current passes through a solenoid, it behaves exactly like a bar magnet with a North pole at one end and a South pole at the other.
Inside the solenoid, the magnetic field lines are uniform, parallel straight lines along its axis.
Outside the solenoid, the field lines emerge from the North pole, curve around, and enter the South pole in closed continuous loops, exactly identical to the field pattern of a bar magnet.
Q8)Solve the following numerical problems:
1. An electric bulb is connected to a 220 V power supply. If the current through the bulb is 0.45 A, what is the power of the bulb?
Answer :
Given: Potential difference V = 220 V, Electric current I = 0.45 A
Formula: Electric Power P = V × I
P = 220 × 0.45 = 99 W
The power of the bulb is 99 Watts.
2. Two coils of resistances 16 Ω each are connected in (i) series and (ii) parallel to a 220 V source. Compare the heat produced in both cases in the same time interval.
The heat produced in parallel connection is 4 times that produced in series connection (Hp : Hs = 4 : 1).
3. An electric iron of 1100 W is operated for 2 hours daily. What will be the electrical energy consumed in the month of April (30 days)? If the cost of electricity is ₹ 5 per unit, find the total bill.
Answer :
Given: Power P = 1100 W = 1.1 kW, Daily time t = 2 hours, Number of days = 30 days
Total time of operation in April: T = 2 × 30 = 60 hours
1. Electrical Energy Consumed:
Energy (E) = P (kW) × T (hours) = 1.1 × 60 = 66 kWh (units)
2. Cost of Electricity:
Rate = ₹ 5 per unit (kWh)
Total cost = 66 × 5 = ₹ 330
Total energy consumed = 66 units; Total bill = ₹ 330.
4. A 100 W bulb is used for 10 hours daily. How many units of electricity does it consume in 1 day?
Answer :
Given: Power P = 100 W = 0.1 kW, Time t = 10 hours
Class 10 Maharashtra State Board Science 1 Chapter 4 explores the thermal and magnetic consequences of electricity. Crucial topics include Joule's Law of Heating, electrical appliances, fuses and MCBs, magnetic field around straight and circular conductors, solenoid magnetic fields, Fleming's Left-Hand and Right-Hand rules, the electric motor, electromagnetic induction, Faraday's laws, AC generators, and domestic AC circuits.
Key Formulas Summary
Joule's Heating Law:H = I²Rt = VIt = (V² / R)t (in Joules)
Electric Power:P = V × I = I²R = V² / R (in Watts)
Q1. What is the fundamental difference between an electric motor and a generator?
An electric motor converts electrical energy into mechanical rotational energy (Fleming's Left-Hand Rule). An electric generator converts mechanical energy into electrical energy via electromagnetic induction (Fleming's Right-Hand Rule).
Q2. What causes short circuits and overloading?
A short circuit occurs when a bare live wire contacts a neutral wire directly, reducing circuit resistance to near zero and causing a dangerous surge in current. Overloading occurs when too many high-power appliances are operated simultaneously on the same circuit.
Q3. What is the purpose of an earth wire in domestic wiring?
The green earth wire connects metal appliance casings to a metal plate buried in the ground. If an insulation fault makes the appliance live, current safely flows into the Earth without shocking the user.
Q4. Why does an alternating current have 50 Hz frequency in India?
A 50 Hz AC current completes 50 complete cycles per second, changing its direction 100 times every second.
Related Study Topics
Effects of Electric Current Class 10Electric Motor ConstructionAC Generator WorkingFleming Left Hand RuleFaraday Law of InductionJoule Heating NumericalsSolenoid Magnetic FieldSSC Board Science 1