What is the difference between series and parallel circuits?

In a series circuit, components are connected end-to-end, so the same current flows through all. In a parallel circuit, components are connected across the same two points, so the voltage is the same across all.

Electricity Exercise Solutions | KalviGavani

Q: State Ohm's law.

At constant temperature, the electric current flowing through a conductor is directly proportional to the potential difference across its ends. V = IR, where V is voltage, I is current, and R is resistance.

I. Choose the Best Answer (MCQs)

Q1. Which of the following is a conductor of electricity?

(a) Rubber (b) Plastic (c) Copper (d) Wood

Answer(c) Copper Copper is a metal and a good conductor of electricity. Rubber, plastic, and wood are insulators that do not allow electric current to pass through them.

Q2. The unit of electric current is

(a) Volt (b) Ohm (c) Ampere (d) Watt

Answer(c) Ampere Electric current is measured in Ampere (A). Volt is the unit of potential difference, Ohm is the unit of resistance, and Watt is the unit of power.

Q3. The device used to measure electric current is

(a) Voltmeter (b) Ammeter (c) Galvanometer (d) Thermometer

Answer(b) Ammeter An ammeter is connected in series with the circuit to measure the current flowing through it. A voltmeter measures potential difference and is connected in parallel.

Q4. In a series circuit, if one bulb fuses, the other bulbs

(a) Glow brighter (b) Continue to glow (c) Do not glow (d) Glow dimmer

Answer(c) Do not glow In a series circuit, all components are in a single path. If one bulb fuses, the circuit breaks and current cannot flow through any component.

Q5. Ohm's law relates

(a) Current and resistance (b) Voltage and current (c) Voltage, current, and resistance (d) Power and current

Answer(c) Voltage, current, and resistance Ohm's law states V = IR, relating voltage (V), current (I), and resistance (R). It shows that voltage equals the product of current and resistance.

Q6. The potential difference is measured in

(a) Ampere (b) Volt (c) Ohm (d) Watt

Answer(b) Volt Potential difference (voltage) is measured in Volts (V). It is the work done to move a unit charge between two points.

Q7. Which of the following is an insulator?

(a) Silver (b) Iron (c) Glass (d) Aluminium

Answer(c) Glass Glass is an insulator that does not allow electric current to pass through it. Silver, iron, and aluminium are metals and good conductors.

Q8. An electric cell has

(a) One terminal (b) Two terminals (c) Three terminals (d) Four terminals

Answer(b) Two terminals An electric cell has two terminals — a positive terminal (metal cap) and a negative terminal (metal disc). Current flows from the positive terminal through the external circuit to the negative terminal.

II. Fill in the Blanks

1. The flow of electric charge through a conductor is called electric current. 2. The SI unit of electric current is ampere. 3. The SI unit of resistance is ohm. 4. A path through which electric current can flow is called an electric circuit. 5. A circuit in which there is no gap is called a closed circuit. 6. A circuit in which there is a gap so that current cannot flow is called an open circuit. 7. The device used to measure potential difference is a voltmeter. 8. The device used to measure electric current is an ammeter. 9. According to Ohm's law, V = I × R. 10. Materials that do not allow electric current to pass through them are called insulators.

III. True or False

Q1. Electric current flows from the negative terminal to the positive terminal outside the cell.

AnswerFalse — In the external circuit, conventional current flows from the positive terminal to the negative terminal of the cell. (Inside the cell, it flows from negative to positive.)

Q2. In a parallel circuit, the voltage across each component is the same.

AnswerTrue — In a parallel circuit, all components are connected across the same two points, so the voltage across each component equals the supply voltage.

Q3. An ammeter is connected in parallel in a circuit.

AnswerFalse — An ammeter is always connected in series with the circuit because it measures the current flowing through the circuit. A voltmeter is connected in parallel.

Q4. Copper is a good conductor of electricity.

AnswerTrue — Copper has low resistance and allows electric current to flow easily, making it widely used in electrical wires.

Q5. A short circuit occurs when the live wire and neutral wire come in direct contact.

AnswerTrue — When live and neutral wires touch without any load (resistance) between them, a large current flows, causing a short circuit. This can lead to overheating and fire.

Q6. Resistance increases with the increase in temperature for a conductor.

AnswerTrue — As temperature increases, atoms in the conductor vibrate more, which obstructs the flow of electrons, increasing the resistance.

IV. Match the Following

Column I	Column II	Answer
Current	Ampere	Current — Ampere
Voltage	Volt	Voltage — Volt
Resistance	Ohm	Resistance — Ohm
Ammeter	Measures current	Ammeter — Measures current
Voltmeter	Measures potential difference	Voltmeter — Measures potential difference

V. Short Answer Questions

Q1. What is an electric circuit? Name its types. Answer: An electric circuit is a closed path through which electric current flows. It consists of a source of electricity (cell/battery), conductors (wires), and a load (bulb/motor).

Types: 1. Closed circuit: A complete path where current flows without interruption. 2. Open circuit: A path with a break/gap where current cannot flow.

Q2. What is the difference between a conductor and an insulator? Give examples. Answer:

Property	Conductor	Insulator
Definition	Allows current to flow	Does not allow current to flow
Resistance	Low	High
Examples	Copper, aluminium, silver	Rubber, plastic, glass, wood

Q3. State Ohm's law and write its formula. Answer: Ohm's law states that at constant temperature, the current flowing through a conductor is directly proportional to the potential difference (voltage) across its ends.

FormulaV = I × R

Where:

V = potential difference (in Volts)
I = current (in Amperes)
R = resistance (in Ohms)

Q4. Define resistance. What is its SI unit? Answer: Resistance is the property of a conductor that opposes the flow of electric current through it. It depends on the material, length, cross-sectional area, and temperature.

SI unit: Ohm (Ω)

Q5. Why is copper wire used as a connecting wire in electric circuits? Answer: Copper wire is used because: 1. Copper is a very good conductor of electricity (has very low resistance). 2. It is ductile — it can be drawn into thin wires. 3. It is relatively inexpensive compared to silver and gold. 4. It is flexible and easy to work with.

Q6. What is a short circuit? Why is it dangerous? Answer: A short circuit occurs when the live wire and neutral wire come in direct contact without any load (resistance) between them. This creates a path of very low resistance, causing a large current to flow, which can overheat the wires and cause fires or damage equipment.

Q7. Distinguish between series and parallel circuits. Answer:

Property	Series Circuit	Parallel Circuit
Current	Same through all components	Different through each component
Voltage	Divided across components	Same across all components
If one fails	All components stop working	Others continue working
Resistance	Adds up (R = R1 + R2 + ...)	Decreases (1/R = 1/R1 + 1/R2 + ...)
Example	Old decorative lights	Household wiring

VI. Detailed Answer Questions

Q1. Explain the construction and working of an electric bell with a diagram description. Answer: Construction: An electric bell consists of: 1. An electromagnet (coil wound on a soft iron core) 2. A hammer (armature) attached to a spring 3. A gong (bell) 4. A contact screw 5. A battery

Working1. When the switch is pressed, current flows through the coil of the electromagnet. 2. The electromagnet becomes magnetised and attracts the iron armature (hammer). 3. The hammer strikes the gong, producing a ringing sound. 4. When the armature is attracted, it moves away from the contact screw, breaking the circuit. 5. The current stops, the electromagnet loses its magnetism, and the spring pulls the armature back. 6. The armature touches the contact screw again, completing the circuit. 7. The process repeats rapidly, causing continuous ringing as long as the switch is pressed.

Q2. Explain the heating effect of electric current and its applications. Answer: Heating Effect: When electric current flows through a conductor with resistance, the conductor gets heated. This is because the electrical energy is converted into heat energy. The amount of heat produced depends on: 1. The current (I) — more current, more heat 2. The resistance (R) — higher resistance, more heat 3. The time (t) — longer time, more heat

FormulaH = I² × R × t (Joule's law of heating)

Applications: 1. Electric iron: A heating element (high-resistance wire) converts electrical energy to heat for pressing clothes. 2. Electric heater: A coil of nichrome wire heats the air or water. 3. Electric kettle: The heating element boils water. 4. Incandescent bulb: The filament (tungsten) gets so hot it glows, producing light. 5. Fuse: A thin wire that melts and breaks the circuit when excessive current flows, protecting appliances.

Q3. Explain the chemical effect of electric current with an example. Answer: Chemical Effect: When electric current passes through a conducting solution (electrolyte), chemical reactions occur at the electrodes. This is called electrolysis.

Example — Electroplating: 1. Take a copper sulphate (CuSO4) solution in a beaker. 2. Connect a copper plate to the positive terminal (anode) and an iron object to the negative terminal (cathode). 3. When current flows, the copper anode dissolves into the solution as Cu²⁺ ions. 4. The Cu²⁺ ions move to the cathode and deposit on the iron object. 5. The iron object gets a thin coating of copper — this is electroplating.

Applications of chemical effects: 1. Electroplating (coating one metal over another) 2. Extraction of metals from ores 3. Purification of metals 4. Electrolytic refining

Q4. Explain the magnetic effect of electric current with an activity. Answer: Magnetic Effect: When electric current flows through a conductor, it produces a magnetic field around it. This is called the magnetic effect of electric current.

Activity (Oersted's experiment): 1. Place a magnetic compass near a straight wire. 2. Note the initial position of the compass needle (pointing north-south). 3. Pass electric current through the wire. 4. Observe that the compass needle deflects from its original position. 5. Reverse the direction of current — the needle deflects in the opposite direction. 6. Increase the current — the deflection increases.

Conclusions:

An electric current produces a magnetic field around the conductor.
The direction of the magnetic field depends on the direction of current.
The strength of the magnetic field increases with increasing current.

Applications: Electromagnets, electric motors, fans, loudspeakers, and MRI machines all work on the magnetic effect of electric current.

Q5. What is a fuse? How does it protect electrical appliances? Answer: A fuse is a safety device made of a thin wire or strip of metal (usually tin-lead alloy) that melts and breaks the circuit when excessive current flows through it.

Working1. The fuse wire is connected in series with the circuit. 2. Under normal conditions, the current flows through the fuse without heating it excessively. 3. When a short circuit or overload occurs, a large current flows through the circuit. 4. The fuse wire heats up beyond its melting point and breaks. 5. The circuit is opened, stopping the current flow and protecting the appliance from damage.

Important points:

Fuse wires are rated for specific current values (e.g., 5A, 15A).
A fuse with the correct rating must be used — too high a rating will not protect the circuit.
Never replace a fuse with a wire of lower resistance (like thick copper wire) as it can cause fire.

Common Mistakes

Confusing series and parallel circuits: In series, current is the same through all components; in parallel, voltage is the same across all components.
Connecting ammeter in parallel: An ammeter must always be connected in series. A voltmeter must be connected in parallel.
Forgetting the direction of conventional current: Conventional current flows from positive to negative in the external circuit.
Confusing resistance units: Resistance is in Ohms (Ω), not Amps or Volts.
Applying Ohm's law at varying temperatures: Ohm's law is valid only at constant temperature. Resistance changes with temperature.
Confusing the three effects of current: Heating effect (iron, heater), chemical effect (electroplating, electrolysis), and magnetic effect (electromagnet, motor) are different phenomena.

Exam Checklist

[ ] Can you define electric current, voltage, and resistance with their units?
[ ] Can you state and apply Ohm's law (V = IR)?
[ ] Can you distinguish between series and parallel circuits?
[ ] Can you identify conductors and insulators with examples?
[ ] Can you explain the heating, chemical, and magnetic effects of electric current?
[ ] Can you describe the construction and working of an electric bell?
[ ] Can you explain what a fuse is and how it protects appliances?
[ ] Can you describe an activity demonstrating the magnetic effect of current?
[ ] Can you explain electroplating as a chemical effect of current?
[ ] Can you solve simple numerical problems using V = IR?

Frequently Asked Questions

A closed path through which electric current flows is called an electric circuit. It consists of a source (cell/battery), a conductor (wire), and a load (bulb).