10th Class Physics Notes 2026 — Chapter 16
Class 10 Physics — Chapter 16: Electricity and Magnetism / Current Electricity
Quran Education Point
Subject: Physics
Class: 10th
Board: Punjab
A. Multiple Choice Questions (MCQs)
16.1 The direction of conventional current is:
(a) From negative to positive terminal
(b) From positive to negative terminal
(c) In both directions at the same time
(d) It does not have a fixed direction
Correct Answer: (b) From positive to negative terminal
16.2 What type of electric current flows in one direction only?
(a) Alternating current
(b) Direct current
(c) Induced current
(d) None of these
Correct Answer: (b) Direct current
16.3 Which device is used to measure electric current?
(a) Voltmeter
(b) Ammeter
(c) Ohmmeter
(d) Wattmeter
Correct Answer: (b) Ammeter
16.4 What is the function of an electromotive force (e.m.f.) source in a circuit?
(a) To reduce resistance in the circuit
(b) To provide energy to drive charges through the circuit
(c) To store electrical energy for later use
(d) To convert electrical energy into mechanical energy
Correct Answer: (b) To provide energy to drive charges through the circuit
16.5 The relationship between voltage, current, and resistance is:
(a) \(V=IR\)
(b) \(V=I/R\)
(c) \(V=I^2R\)
(d) \(V=R/I\)
Correct Answer: (a) \(V=IR\)
16.6 What happens to the resistance of a metal conductor when its temperature increases?
(a) It decreases
(b) It remains constant
(c) It increases
(d) It becomes zero
Correct Answer: (c) It increases
B. Short Answer Questions
16.1 How does an ammeter measure electric current?
Answer:
An ammeter measures electric current by allowing the circuit’s charge to pass through it. It is always connected in series with the circuit component so that the entire current flows through it.
An ammeter has very low internal resistance to ensure that it does not significantly change or restrict the current flowing in the circuit.
16.2 What is the main difference between direct current and alternating current?
Answer:
Direct Current (D.C.): Electric current that flows in only one direction with constant polarity, such as current supplied by batteries or cells.
Alternating Current (A.C.): Electric current that periodically reverses its direction and changes its magnitude with time, such as the mains electricity supply in homes.
16.3 Define electromotive force (e.m.f.).
Answer:
Electromotive force (e.m.f.) is the energy supplied by a battery or source per unit charge passing through a complete circuit.
Where:
\(E\) = Electromotive force
\(W\) = Energy supplied or work done
\(Q\) = Electric charge
SI Unit: Volt (V), or joule per coulomb (J/C).
16.4 State Ohm’s law and define resistivity.
Answer:
Ohm’s Law: The current flowing through a conductor is directly proportional to the potential difference across its ends, provided its physical conditions and temperature remain constant.
Where \(V\) is voltage, \(I\) is current, and \(R\) is resistance.
Resistivity \((\rho)\): Resistivity is a property of a material that measures how strongly it opposes the flow of electric current. It is defined as the resistance of a conductor of unit length and unit cross-sectional area.
Where:
\(\rho\) = Resistivity
\(R\) = Resistance
\(A\) = Cross-sectional area
\(L\) = Length of the conductor
SI Unit: Ohm-metre \((\Omega\cdot\text{m})\).
16.5 What is the formula for calculating the equivalent resistance of resistors connected in series?
Answer:
For \(n\) resistors connected in series, the equivalent resistance is the sum of their individual resistances.
16.6 How does temperature affect the resistance of a conductor?
Answer:
As the temperature of a metallic conductor increases, the thermal vibrations of its atoms increase. This causes more frequent collisions between free electrons and atoms, making the flow of electrons more difficult.
Consequently, the resistance of a metallic conductor increases with an increase in temperature.
C. Constructed Response Questions
16.1 Why is it important that an ammeter has very low resistance and is connected in series, while a voltmeter has very high resistance and is connected in parallel? What would happen if they were connected incorrectly?
Answer:
Ammeter:
Why connected in series: An ammeter measures the current flowing through a circuit component. It must be connected in series so that the same current passes through it.
Why it has low resistance: Its very low resistance prevents it from significantly reducing the circuit current.
Incorrect connection: Connecting an ammeter in parallel can create a short circuit because of its low resistance. This may cause excessive current, blow a fuse, or damage the ammeter and power supply.
Voltmeter:
Why connected in parallel: A voltmeter measures the potential difference between two points, so it is connected across the component.
Why it has high resistance: Its high resistance ensures that it draws negligible current and does not significantly disturb the circuit.
Incorrect connection: Connecting a voltmeter in series greatly restricts current flow because of its high resistance, preventing the circuit from functioning properly.
16.2 If a copper wire is replaced with an aluminium wire of the same dimensions, how would the current and power consumption change in the same circuit? Explain using the concept of resistivity.
Answer:
Resistivity Comparison:
Aluminium has a higher resistivity than copper.
Effect on Resistance:
The resistance of a wire is given by:
For wires of identical length and cross-sectional area, replacing copper with aluminium increases the resistance.
Effect on Current:
According to Ohm’s law,
At the same supply voltage, an increase in resistance reduces the current flowing through the circuit.
Effect on Power Consumption:
At constant voltage,
Therefore, if the resistance increases, the power dissipated in the wire decreases, assuming the supply voltage remains constant.
16.3 In a household lighting circuit, what practical problems might arise if the bulbs were connected in series instead of parallel?
Answer:
Single Point of Failure: If one bulb breaks or burns out, the circuit opens and all the other lights turn off.
Reduced Brightness: Adding more bulbs in series increases the total resistance and reduces the current. The voltage is divided among the bulbs, making them glow more dimly.
Lack of Independent Control: Individual switches cannot operate each bulb independently. All bulbs must be switched on or off together unless additional circuit arrangements are used.
16.4 You are tasked with designing a fuse for a device that operates at 230 V and 5 A. What rating would you choose for the fuse and why? What could go wrong if the rating is too low or too high?
Answer:
Chosen Fuse Rating: A fuse rated slightly above the normal operating current should be selected. The supplied solution suggests a rating of 6 A or 7 A, subject to the device manufacturer’s specifications and applicable safety requirements.
Reason: The fuse should allow the normal operating current of 5 A to flow without unnecessary melting while interrupting excessive current during a fault.
If the Rating Is Too Low: For example, a 3 A fuse may melt during normal operation, preventing the device from functioning properly.
If the Rating Is Too High: For example, a 20 A fuse may fail to protect the device adequately during an overload, increasing the risk of overheating, fire, or appliance damage.
16.5 Explain why A.C. is more suitable for power transmission across cities, even though D.C. is used in batteries and portable electronic devices.
Answer:
Voltage Transformation: A.C. voltage can be stepped up or down easily using transformers. It can be increased to high voltages for transmission and reduced for distribution and domestic use.
Minimizing Energy Losses: Transmitting electrical energy at high voltage reduces current for a given power. Since power loss in transmission lines is given by
lower current greatly reduces energy losses.
3. Cost Efficiency: Lower transmission current can reduce the required conductor size for a given loss limit, helping make power transmission more economical.
D.C. is commonly used in batteries and portable electronic devices because batteries supply direct current. Modern high-voltage D.C. transmission is also used in some applications, but A.C. is widely used in conventional power grids because voltage transformation is straightforward.
D. Comprehensive Questions
16.1 Explain the concept of electric current. How is it related to the movement of charges, and how is it measured in a circuit?
Answer:
Definition of Electric Current:
Electric current is the rate of flow of electric charge through any cross-section of a conductor per unit time.
Where:
\(I\) = Electric current in amperes (A)
\(Q\) = Electric charge in coulombs (C)
\(t\) = Time in seconds (s)
Relation to Charge Movement:
In metallic conductors, electric current is produced by the directed movement of free electrons. The electrons move opposite to the direction of conventional current. In solutions and gases, current can also be carried by positive and negative ions.
Measurement:
Current is measured using an ammeter connected in series with the circuit component so that the current passes through it.
16.2 Define electromotive force (e.m.f.) and potential difference. How does a battery create a potential difference, and what is the role of e.m.f. in maintaining the flow of current?
Answer:
Electromotive Force (e.m.f.):
Electromotive force is the energy supplied by a source per unit charge. A battery uses chemical energy to move charges internally and maintain a potential difference between its terminals.
Potential Difference (P.D.):
Potential difference between two points is the energy transferred per unit charge as charge moves between those points.
How a Battery Creates Potential Difference:
Chemical reactions inside a battery separate charges, establishing a higher electric potential at the positive terminal and a lower potential at the negative terminal.
Role of e.m.f.:
The e.m.f. supplies energy to charges and maintains the potential difference needed to drive current through a complete circuit.
16.3 State and explain Ohm’s law. How does the resistance of a conductor affect the flow of current, and how can Ohm’s law be applied in practical electrical circuits?
Answer:
Ohm’s Law:
The current flowing through a conductor is directly proportional to the potential difference across its ends, provided its physical conditions and temperature remain constant.
Therefore,
Where \(V\) is potential difference, \(I\) is current, and \(R\) is resistance.
Effect of Resistance:
Resistance opposes the flow of electric current. At a fixed voltage, higher resistance produces lower current, while lower resistance allows greater current.
Practical Applications:
Designing current-limiting resistors to protect sensitive electronic components.
Calculating the required ratings of electrical components, including heater elements.
Determining power supply requirements for specific electrical loads.
16.4 Differentiate between series and parallel combinations of resistors. Provide mathematical expressions for calculating the total resistance in both types of circuits.
Answer:
Feature | Series Combination | Parallel Combination |
|---|---|---|
Path for current | Only one path | Multiple paths |
Current | Same through each resistor: \(I=I_1=I_2\) | Divides among branches: \(I=I_1+I_2+\cdots\) |
Voltage | Divides across resistors: \(V=V_1+V_2+\cdots\) | Same across each branch: \(V=V_1=V_2=\cdots\) |
Equivalent resistance | \(R_{\text{eq}}=R_1+R_2+R_3+\cdots\) | \(\frac{1}{R_{\text{eq}}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\cdots\) |
Total resistance | Greater than any individual resistance | Less than the smallest individual resistance |
16.5 What is meant by resistivity of a material? How does it depend on the material, and what role does temperature play in changing the resistivity of conductors and semiconductors?
Answer:
Resistivity \((\rho)\):
Resistivity is an intrinsic property of a material that describes how strongly it opposes the flow of electric current. It is given by:
Where:
\(\rho\) = Resistivity
\(R\) = Resistance
\(A\) = Cross-sectional area
\(L\) = Length of the conductor
Dependence on Material:
Resistivity depends on the material’s atomic structure and the availability and behaviour of charge carriers. Metals generally have low resistivity, while insulating materials have very high resistivity.
Effect of Temperature:
Conductors: The resistivity of most metals increases with temperature because increased atomic vibrations impede the movement of free electrons.
Semiconductors: Their resistivity generally decreases with temperature because heating creates more charge carriers, including electron-hole pairs.
E. Numerical Problems
Problem 16.1
A charge of 25 coulombs passes through a circuit in 10 seconds. Calculate the current flowing through the circuit.
Given Data:
Charge, \(Q=25\,\text{C}\)
Time, \(t=10\,\text{s}\)
To Find:
Current, \(I=?\)
Formula:
Calculation:
Answer:
Current flowing through the circuit is \(2.5\,\text{A}\).
Problem 16.2
Three resistors of \(4\,\Omega\), \(6\,\Omega\), and \(8\,\Omega\) are connected in series to a 24 V battery. Find the total resistance and the current flowing through the circuit.
Given Data:
\(R_1=4\,\Omega\)
\(R_2=6\,\Omega\)
\(R_3=8\,\Omega\)
Voltage, \(V=24\,\text{V}\)
To Find:
Total resistance, \(R_{\text{eq}}=?\)
Current, \(I=?\)
Formulae:
For series resistors,
Using Ohm’s law,
Calculation:
Step 1: Calculate total resistance.
Step 2: Calculate current.
Answer:
Total resistance = \(18\,\Omega\)
Current = \(1.33\,\text{A}\)
Problem 16.3
Two resistors of \(10\,\Omega\) and \(30\,\Omega\) are connected in parallel across a 20 V power supply. Calculate the total resistance and the current drawn from the power supply.
Given Data:
\(R_1=10\,\Omega\)
\(R_2=30\,\Omega\)
Voltage, \(V=20\,\text{V}\)
To Find:
Total resistance, \(R_{\text{eq}}=?\)
Total current, \(I=?\)
Formulae:
For two resistors in parallel,
Therefore,
Using Ohm’s law,
Calculation:
Step 1: Calculate total resistance.
Step 2: Calculate total current.
Answer:
Total resistance = \(7.5\,\Omega\)
Current drawn = \(2.67\,\text{A}\)
Problem 16.4
Four 1.5 V batteries are connected in series in a flashlight. Determine the total electromotive force (e.m.f.) supplied to the circuit.
Given Data:
Voltage of each battery, \(E_1=E_2=E_3=E_4=1.5\,\text{V}\)
Number of batteries, \(n=4\)
To Find:
Total e.m.f., \(E_{\text{total}}=?\)
Formula:
For batteries connected in series with the same polarity,
Or,
Calculation:
Answer:
Total e.m.f. supplied to the circuit is \(6\,\text{V}\).
Problem 16.5
A circuit has a 5 A current passing through a \(7\,\Omega\) resistor. Calculate the power dissipated in the resistor and the energy consumed in 10 minutes.
Given Data:
Current, \(I=5\,\text{A}\)
Resistance, \(R=7\,\Omega\)
Time, \(t=10\,\text{minutes}=10\times60=600\,\text{s}\)
To Find:
Power dissipated, \(P=?\)
Energy consumed, \(W=?\)
Formulae:
Power dissipated in a resistor:
Energy consumed:
Calculation:
Step 1: Calculate power.
Step 2: Calculate energy consumed.
Converting joules into kilojoules:
Answer:
Power dissipated = \(175\,\text{W}\)
Energy consumed = \(105\,\text{kJ}\)
Notes by Sir Dilawar
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