CBSE Class 7 Science Advanced Physics Electricity Very Short Answer Questions Set 01

Very Short Answer Questions

Question 1. Fill in the blank.
The most convenient form of energy is _______ energy.
Answer:
electrical
In simple words: Electrical energy is the form that is easiest to carry and convert to others.

Teacher's Note:
1. It can travel along wires and be changed into light, heat or motion.
2. This is why the chapter starts with it.

Question 2. Fill in the blank.
When two bodies A and B are rubbed, they acquire charge by friction. If the charge on A is positive, then the charge on B is ______.
Answer:
negative
In simple words: Rubbing gives two equal and opposite charges.

Teacher's Note:
1. Electrons move from one body to the other, so one becomes positive and the other negative.
2. The charges are equal in size.

Question 3. Fill in the blank.
_______ is a device used to detect the presence and the nature of the charge on a body.
Answer:
Electroscope (gold leaf electroscope)
In simple words: An electroscope shows whether a body has charge and of what kind.

Teacher's Note:
1. The strips of the electroscope move apart or come together.
2. Do not confuse it with the electric bell or the galvanoscope.

Question 4. Fill in the blank.
_______ is used to protect buildings from lightning.
Answer:
Lightning conductor
In simple words: A thick metal strip with a pointed top leads the charge to the earth.

Teacher's Note:
1. It carries the discharge safely into the ground.
2. Remember its plate buried in the earth.

Question 5. Fill in the blank.
When charges are moving from one end to the other end of a conductor, we say there is _______ in the conductor.
Answer:
electric current
In simple words: Moving charge in a conductor is a current.

Teacher's Note:
1. Charges at rest are studied in electrostatics.
2. Current is the basis of all uses of electricity.

Question 6. Fill in the blank.
_______ acts as a positive pole and _______ as a negative pole in a dry cell.
Answer:
Carbon rod (with its brass cap) acts as the positive pole and zinc can as the negative pole.
In simple words: In a dry cell the carbon rod is +, the zinc container is −.

Teacher's Note:
1. The brass cap on top of the carbon rod is the + terminal.
2. The zinc can also serves as the container.

Question 7. Fill in the blank.
_________ and _________ are two defects of voltaic cell.
Answer:
Polarization and local action
In simple words: The voltaic cell loses power because of hydrogen bubbles and impure zinc.

Teacher's Note:
1. A depolariser cures polarization; a mercury coating cures local action.
2. Learn the remedy together with each defect.

Question 8. Fill in the blank.
Four cells of e.m.f 2.5 V each are connected in series to form a battery, the e.m.f of the battery is ________.
Answer:
10 V
In series the e.m.f. is added: 2.5 + 2.5 + 2.5 + 2.5 = 10 V.
In simple words: Adding four equal cells of 2.5 V gives 10 V.

Teacher's Note:
1. Series connection adds the e.m.f. of the cells.
2. Check the arithmetic: 4 × 2.5 = 10.

Question 9. Fill in the blank.
________ or ________ is used to protect electrical appliances from damages due to excess current.
Answer:
Fuse or miniature circuit breaker (MCB)
In simple words: A fuse or an MCB cuts off the current when it becomes too large.

Teacher's Note:
1. A fuse melts and has to be replaced, but an MCB can be switched on again.
2. Both are fixed in series with the live wire.

Question 10. Fill in the blank.
When electric current passes through a wire, ________ field is created around it.
Answer:
magnetic
In simple words: A current always carries a magnetic field around its wire.

Teacher's Note:
1. This is the magnetic effect of electric current.
2. It was discovered by Oersted.

Teacher's Note:
1. The pairing of electric power with the eel fish follows the book: the eel produces electricity in its body.
2. Franklin proved that lightning is an electric discharge and designed the lightning rod.

Teacher's Note:
1. Closed tap key: a continuous line with two dots.
2. The fuse wire melts because of the heating effect.

Question 13. How many types of charges are there and what are they?
Answer:
There are two types of charges: positive charge and negative charge.
In simple words: Nature has only a positive and a negative charge.

Teacher's Note:
1. Like charges repel and unlike charges attract.
2. Every charged body has one of these two kinds.

Question 14. What is an ‘electron’?
Answer:
An electron is the negatively charged particle present in an atom. It can move freely within a body and from one body to another.
In simple words: The electron is the small negative particle that can move around.

Teacher's Note:
1. Electrons are responsible for charging by friction and conduction.
2. The atom as a whole is neutral.

Question 15. What is an electroscope?
Answer:
An electroscope is an instrument that detects the presence of charge on a body and shows what kind of charge it is.
In simple words: The electroscope tells us whether and how a body is charged.

Teacher's Note:
1. In a gold leaf electroscope the strips open when they are charged.
2. Know its parts: cap, rod, jar and strips.

Question 16. When do we say that there is an electric current in a conductor?
Answer:
When charges move from one end of the conductor to the other, an electric current flows in it.
In simple words: Moving charge in a wire is an electric current.

Teacher's Note:
1. Charges at rest give no current.
2. A switch is used to start or stop this flow.

Question 17. What is an electric circuit?
Answer:
An electric circuit is the path along which electric current flows, from the source through the appliances and back to the source.
In simple words: A circuit is the route that the current takes.

Teacher's Note:
1. It is drawn using standard symbols in a circuit diagram.
2. A circuit may be open or closed.

Question 18. What is a switch?
Answer:
A switch is a device used to make or break (close or open) an electric circuit.
In simple words: A switch turns a circuit on or off.

Teacher's Note:
1. ON means closed circuit and OFF means open circuit.
2. A switch is always fitted on the live wire.

Question 19. Name two different ways of connecting components in an electric circuit.
Answer:
Components can be connected in series and in parallel.
In simple words: Two ways: one after another, or side by side.

Teacher's Note:
1. In series there is a single path.
2. In parallel there are branches.