Willer Academy - Electricity and Circuits

Willer Academy

Nation Builders Through Education | Founded by Er. Rahul Kumar Dubey Sir

Chapter 12: Electricity and Circuits

Subject: Science (Physics)

Class: 7

Series: Base Builder for Moderate to Hard

Learning Objectives

By the end of this chapter, you, the future scientist and nation-builder, will be able to:

Understand the basic concepts of electricity and electric current
Differentiate between conductors and insulators
Explain the components of an electric circuit and their symbols
Build simple series and parallel circuits
Apply Ohm's Law to solve simple circuit problems
Understand electrical safety measures
Apply knowledge to real-life electrical applications

12.1 Introduction: What is Electricity?

Electricity is a form of energy resulting from the existence of charged particles (such as electrons or protons), either statically as an accumulation of charge or dynamically as a current.

Current

Flow of electric charge

Measured in Amperes (A)

Voltage

Electrical potential difference

Measured in Volts (V)

Resistance

Opposition to current flow

Measured in Ohms (Ω)

Quick Check

Think about how electricity helps you perform daily activities. What would a day without electricity be like?

12.2 Electric Circuits

An electric circuit is a path through which electric current flows. A complete circuit must have a power source, conductors, and a load.

Battery

Power source

| |

Bulb

Load/Output device

(x)

Switch

Controls current flow

Resistor

Limits current

/\/\/\

Experiment: Building a Simple Circuit

Using a battery, two wires, and a small bulb, create a simple circuit that lights the bulb. Draw a diagram of your circuit using proper symbols. What happens if you add a switch? Try it and observe.

12.3 Series and Parallel Circuits

Circuits can be arranged in different configurations, each with unique properties.

Series Circuit

Components connected end-to-end
Single path for current
Current same everywhere
Voltage divides among components
If one component fails, circuit breaks

Parallel Circuit

Components connected across same points
Multiple paths for current
Voltage same across all components
Current divides among paths
If one component fails, others still work

Numerical & Application 1: Circuit Analysis

Scenario: Two bulbs with resistances of 10Ω and 20Ω are connected in series to a 6V battery.
Problem: Calculate the total resistance, current in the circuit, and voltage across each bulb.
Solution:
- Total resistance R = R₁ + R₂ = 10Ω + 20Ω = 30Ω
- Current I = V/R = 6V/30Ω = 0.2A
- Voltage across first bulb V₁ = I × R₁ = 0.2A × 10Ω = 2V
- Voltage across second bulb V₂ = I × R₂ = 0.2A × 20Ω = 4V

This demonstrates how voltage divides in a series circuit!

12.4 Conductors and Insulators

Materials behave differently when it comes to conducting electricity.

Conductors	Insulators
Allow electric current to flow easily	Do not allow electric current to flow
Have free electrons	Have tightly bound electrons
Examples: Copper, Aluminum, Silver	Examples: Rubber, Plastic, Glass
Used for wires and connections	Used for insulation and safety covers

Task 1: Material Investigation

Test various materials (coin, paper clip, rubber band, pencil lead, plastic ruler) with a simple circuit to determine if they are conductors or insulators. Create a table of your findings.

12.5 Electrical Safety

Electricity is extremely useful but can be dangerous if not handled properly.

Important Safety Measures

Dry Hands

Never touch electrical devices with wet hands

No Metal Objects

Don't insert metal objects into electrical outlets

Fuse Protection

Circuits should have proper fuses to prevent overload

Professional Help

Get professional help for electrical repairs

Experiment: Simple Fuse Simulation

Create a circuit with a thin strand of steel wool that acts as a fuse. When too much current flows, the steel wool will heat up and break, interrupting the circuit. This demonstrates how fuses protect circuits.

Safety Note: Perform this experiment under adult supervision only.

12.6 Ohm's Law

Ohm's Law defines the relationship between voltage, current, and resistance in an electrical circuit.

V = I × R

Where:

V = Voltage (Volts)

I = Current (Amperes)

R = Resistance (Ohms)

Numerical & Application 2: Ohm's Law

Scenario: A circuit has a resistance of 100Ω and a current of 0.5A flowing through it.
Problem: What is the voltage of the battery? If we replace the battery with a 200V source, what will be the new current?
Solution:
- Voltage V = I × R = 0.5A × 100Ω = 50V
- New current I = V/R = 200V/100Ω = 2A

This demonstrates the direct relationship between voltage and current when resistance is constant!

Section B: MCQ Challenge (20 Questions)

Test your knowledge and find where you need to improve!

1. Which of the following is a good conductor of electricity?

a) Rubber

b) Plastic

c) Copper

d) Wood

2. In a series circuit, if one bulb burns out:

a) The other bulbs get brighter

b) The other bulbs stay lit

c) All other bulbs go out

d) The battery voltage increases

3. According to Ohm's Law, if voltage doubles and resistance remains constant:

a) Current halves

b) Current doubles

c) Current remains the same

d) Resistance doubles

4. In a parallel circuit, the voltage across each branch is:

a) Different for each branch

b) Zero

c) Depends on current

d) The same across all branches

5. Which material is typically used for electrical insulation?

a) Rubber

b) Copper

c) Aluminum

d) Silver

6. What happens to the total resistance when more resistors are added in series?

a) Decreases

b) Stays the same

c) Increases

d) Becomes zero

7. The device used to measure electric current is called:

a) Voltmeter

b) Ammeter

c) Ohmmeter

d) Wattmeter

8. Which of the following is true for a series circuit?

a) Voltage same across all components

b) Current divides among components

c) Components are connected across same points

d) Current same everywhere

9. When a fuse blows in a circuit:

a) Circuit gets disconnected

b) Current increases

c) Voltage increases

d) Resistance becomes zero

10. What is the unit of electric current?

a) Volt

b) Ohm

c) Ampere

d) Watt

11. Which of the following affects the resistance of a wire?

a) Length of wire

b) Cross-sectional area

c) Material of wire

d) All of the above

12. The symbol "-" in a circuit diagram represents:

a) Switch

b) Resistor

c) Bulb

d) Battery terminal

13. A material that does not allow current to pass through is called:

a) Insulator

b) Conductor

c) Semiconductor

d) Electrolyte

14. The current in a parallel circuit:

a) Is the same in all branches

b) Divides among the branches

c) Is zero

d) Depends on battery voltage only

15. The primary function of a switch in a circuit is to:

a) Increase voltage

b) Decrease resistance

c) Control the flow of current

d) Store energy

16. Which of the following is an example of a conductor?

a) Plastic ruler

b) Wooden stick

c) Silver coin

d) Glass

17. Which factor does NOT affect resistance of a wire?

a) Temperature

b) Length of wire

c) Colour of insulation

d) Cross-sectional area

18. Total voltage in a series circuit:

a) Is same as one component

b) Divides among components

c) Is zero

d) Depends on current only

19. The function of a resistor in a circuit is to:

a) Increase current

b) Limit current

c) Store energy

d) Generate voltage

20. Which device measures voltage in a circuit?

a) Ammeter

b) Voltmeter

c) Ohmmeter

d) Wattmeter

Answers: 1-c, 2-c, 3-b, 4-d, 5-a, 6-c, 7-b, 8-d, 9-a, 10-c, 11-d, 12-d, 13-a, 14-b, 15-c, 16-c, 17-c, 18-b, 19-b, 20-b

Section C: Answer in Detail (For Answer Writing Practice)

Q1. Explain the differences between series and parallel circuits with diagrams. Give two examples of where each type is used in real life.

Hint: Include current paths, voltage distribution, and practical applications.

Q2. Describe Ohm's Law and use it to solve the following problem: A circuit has a 12V battery and a current of 0.3A. What is the resistance? If we want to double the current, what should we do?

Hint: Include the formula, calculations, and explanation of the relationship between variables.

Q3. Why are electrical safety measures important? List five safety rules that should be followed when working with electricity.

Hint: Include potential dangers and preventive measures.

Section D: Tackle These! (Higher Order Thinking Skills - HOTS)

Q1. Design a circuit for a room with three bulbs and a fan that can be controlled independently. Draw the circuit diagram and explain why you chose this configuration.

Think about: Circuit type, control mechanisms, and practical considerations.

Q2. Why are metals good conductors of electricity while non-metals are generally insulators? Explain at the atomic level.

Think about: Electron configuration, free electrons, and atomic structure.

Q3. Imagine you have two identical bulbs. When connected in series to a battery, they glow dimly. When connected in parallel to the same battery, they glow brightly. Explain this phenomenon.

Think about: Voltage distribution, current paths, and power consumption.