Class 7 Science Worksheet on Electricity and Magnetism | Set 14
This Class 7 Science Worksheet on Electricity and Magnetism covers essential topics such as circuits, solenoids, fuses, resistance, and electrolysis. Designed to align with the CBSE and NCERT curriculum, this worksheet helps students understand the core concepts of electricity and magnetism while preparing them for exams and real-world applications.Q1: Answer the Following Questions
a. Why are filament-type electric bulbs not power-efficient? Name two energy-efficient alternatives.
Filament-type electric bulbs waste most of their energy as heat rather than light, making them inefficient. Two energy-efficient alternatives are:
- LED (Light Emitting Diode) bulbs
- CFL (Compact Fluorescent Lamp) bulbs
b. What is a Fuse and Why is it Important?
i. What is the purpose of a fuse in a circuit?
A fuse is a safety device that protects electrical circuits by melting and breaking the circuit when there is an overload or short circuit, preventing damage to appliances and potential fires.
ii. What happens if a fuse is missing?
Without a fuse, excessive current can flow through the circuit, leading to overheating, fires, or damage to connected devices.
c. Why is an electrolyte necessary for electrolysis? Can pure water undergo electrolysis?
An electrolyte is necessary because it provides free ions that conduct electricity during electrolysis. Pure water cannot undergo electrolysis effectively because it lacks sufficient free ions. Adding an electrolyte like salt or acid is required to enable the process.
d. Why does resistance increase with temperature in a conductor?
As temperature increases, the atoms in a conductor vibrate more vigorously, obstructing the flow of electrons. This increased obstruction results in higher resistance.
Q2: Case Study – Lifting Heavy Objects with Solenoids
In factories, solenoids (electromagnets) powered by batteries are used to lift heavy metal objects efficiently.a. Why use a solenoid instead of a permanent magnet?
Solenoids are preferred because they can be turned on and off, providing better control over lifting and releasing objects. Permanent magnets, on the other hand, cannot be deactivated easily.
b. What happens if the solenoid is disconnected from the battery?
When disconnected, the solenoid loses its magnetic field, causing the metal object to fall.
c. How can the solenoid lift heavier objects?
To lift heavier objects:
- Increase the number of coils in the solenoid.
- Use a stronger battery to increase the current and strengthen the magnetic field.
Real-Life Applications of Electricity and Magnetism
- Electricity powers everyday devices like lights, fans, computers, and industrial machinery.
- Magnetism is used in motors, generators, and magnetic cranes.
- Electromagnets are widely used in recycling plants to separate metal objects from waste.
FAQs
1. What are the two industries where electromagnets are widely used?
Electromagnets are widely used in the automotive industry (e.g., in car lifts) and the recycling industry (e.g., for separating metals).2. Why are CFLs preferred over filament bulbs?
CFLs are preferred because they are more energy-efficient, produce less heat, and have a longer lifespan compared to filament bulbs.3. What is the SI unit of resistance?
The SI unit of resistance is the Ohm (Ω).1. What is the difference between an electromagnet and a permanent magnet?
An electromagnet is a temporary magnet that works only when electric current flows through it. A permanent magnet, like a bar magnet, retains its magnetism without an external power source.
2. How does a circuit breaker work?
A circuit breaker automatically interrupts the flow of current when it detects an overload or short circuit, preventing damage to the circuit and appliances.
3. What is the role of resistance in a circuit?
Resistance controls the flow of current in a circuit. It is measured in ohms (Ω) and ensures that devices receive the correct amount of current.