CBSE Class 7 Science Advanced Physics Electricity Very Short Answer Questions Set 02

Very Short Answer Questions

Question 1. How many types of sockets are in use and what are they?
Answer:
Two types: the two-pin socket and the three-pin socket. The third pin of the three-pin socket is the earth pin.
In simple words: There are 2-pin and 3-pin sockets.

Teacher's Note:
1. Appliances with metal bodies use a three-pin plug for safety.
2. The earth pin carries any leaking current to the ground.

Question 2. What is a miniature circuit breaker? Where is it used?
Answer:
A miniature circuit breaker (MCB) is a switch that automatically turns off when the current in a circuit exceeds a safe limit. It is joined in series with the live wire in household circuits and is a good substitute for a fuse.
In simple words: An MCB trips off when too much current flows.

Teacher's Note:
1. After the fault is cleared the MCB can be switched on again.
2. A fuse wire, in contrast, has to be replaced after it melts.

Question 3. What is the e.m.f of the Bichromate cell?
Answer:
The e.m.f. of the bichromate cell is 2 V.
In simple words: The bichromate cell gives 2 volts.

Teacher's Note:
1. Compare it with the 1.46 V of the dry cell.
2. Its electrolyte is potassium dichromate in dilute sulphuric acid.

Question 4. How can we describe the force between two charged bodies?
Answer:
The force is repulsive between like charges and attractive between unlike charges.
In simple words: Like charges push apart; unlike charges pull together.

Teacher's Note:
1. This follows from the activity with glass and ebonite rods.
2. The force is called the electrostatic force.

Question 5. Which charged particle is free to move within the body as well as from one body to another body?
Answer:
The electron (negatively charged particle).
In simple words: Only electrons can move around; the positive charges stay in place.

Teacher's Note:
1. That is why we say a body is positive when it has lost electrons.
2. Remember this for charging by friction.

Teacher's Note:
1. Conductors have free electrons; insulators have almost none.
2. Plastic covering on wires protects us from shocks.

Question 7. Write any two sources of electrical energy.
Answer:
Cell (or battery) and electric generator.
In simple words: Cells and generators give electrical energy.

Teacher's Note:
1. Cells use chemical energy and generators use mechanical energy.
2. Button cells and car batteries are also sources.

Question 8. What is a battery?
Answer:
A battery is a combination of two or more cells connected together to get a larger e.m.f.
In simple words: Several cells joined together make a battery.

Teacher's Note:
1. Cells in a battery are usually joined in series.
2. Positive to negative, one after the other.

Question 9. What is an electric generator?
Answer:
An electric generator is a device that converts mechanical energy into electrical energy. It has a turbine and a dynamo; the turbine turns the dynamo, which produces electricity.
In simple words: A generator produces electricity from motion.

Teacher's Note:
1. Moving water or steam turns the turbine.
2. It is used in power plants.

Question 10. What is ‘one unit’ or ‘one kilowatthour’ of electrical energy?
Answer:
One unit (1 kW h) is the electrical energy used by an appliance of power 1000 W in one hour.
1 unit = 1 kW h = 1000 × 60 × 60 J = 3.6 × 10⁶ J.
In simple words: One unit is what a 1000 W appliance uses in an hour.

Teacher's Note:
1. Electricity bills are based on the number of units.
2. A 100 W bulb takes 10 hours to use one unit.

Question 11. What is a fuse?
Answer:
A fuse is a safety device that prevents an excess current from flowing through an appliance. Its thin wire melts when the current is too large and breaks the circuit.
In simple words: A fuse cuts the circuit when the current is too much.

Teacher's Note:
1. Its wire is made of a metal that melts easily.
2. It works on the heating effect of current.

Question 12. What happens when current passes through an electrolyte?
Answer:
Chemical changes take place. The electrolyte splits into ions, which move towards the oppositely charged electrodes. This process is called electrolysis.
In simple words: Current breaks the electrolyte into ions.

Teacher's Note:
1. This is the chemical effect of electric current.
2. Electroplating is an application.

Question 13. Why are thick wires used in fuses?
Answer:
A thicker fuse wire has less resistance and can carry a larger current without melting. Circuits and appliances that draw more current therefore need a thicker fuse wire, which melts only when the current goes beyond the safe value for that circuit.
In simple words: The thickness of the fuse wire is chosen to match how much current the appliance needs.

Teacher's Note:
1. A thin wire would melt even in normal use of a heavy appliance.
2. A thick wire in a small circuit would not protect it.

Question 14. State whether the following statement is true or false.
A neutral body means a body with no charged particles on it.
Answer:
False. A neutral body contains both positive and negative particles in equal numbers, so the total charge is zero.
In simple words: Neutral does not mean empty of charge; it means the charges balance.

Teacher's Note:
1. Atoms are neutral because positive and negative charges are equal.
2. Charging only changes the balance.

Question 15. State whether the following statement is true or false.
The charged particle in an atom that contributes positive charge is ‘electron‘.
Answer:
False. The electron is the negatively charged particle of an atom.
In simple words: Electrons are negative; positive charge comes from other particles.

Teacher's Note:
1. Remember the electron by its negative sign.
2. Only the electrons move in charging.

Question 16. State whether the following statement is true or false.
Substances which allow charges to pass through them are called conductors.
Answer:
True.
In simple words: This is the definition of a conductor.

Teacher's Note:
1. Metals are good conductors.
2. Insulators block the flow of charge.

Question 17. State whether the following statement is true or false.
A Switch is used to make or break an electric circuit.
Answer:
True. A switch closes (makes) or opens (breaks) the circuit.
In simple words: A switch connects or disconnects the circuit.

Teacher's Note:
1. The word ‘brake’ in the book is a spelling mistake for ‘break’.
2. ON means the circuit is closed.

Question 18. State whether the following statement is true or false.
The Zinc plate in a voltaic cell is usually coated with mercury to prevent polarization.
Answer:
False. The mercury coating prevents local action. Polarization is reduced by using a depolariser.
In simple words: Mercury stops local action, not polarization.

Teacher's Note:
1. Local action: impurities in zinc; polarization: hydrogen bubbles.
2. Do not mix the two remedies.

Question 19. State whether the following statement is true or false.
When bulbs are connected to the same source, the brightness of bulbs connected in series is more than the brightness of identical bulbs connected in parallel.
Answer:
False. Bulbs in parallel are brighter, because each gets the full supply, whereas bulbs in series share the energy.
In simple words: Parallel bulbs are brighter than series bulbs.

Teacher's Note:
1. Series: shared energy, dim bulbs.
2. Parallel: full energy, bright bulbs.