CBSE Class 7 Science Advanced Physics Electricity Very Short Answer Questions Set 03

Very Short Answer Questions

Question 1. State whether the following statement is true or false.
In household connections, no current passes through neutral wire when the switch is off.
Answer:
True. The switch is on the live wire, so when it is off the circuit is open and no current flows in either wire.
In simple words: The switch is on the live wire, so turning it off stops the current everywhere.

Teacher's Note:
1. An open circuit carries no current.
2. Still, never touch the live wire.

Question 2. State whether the following statement is true or false.
Connecting many devices to a single socket leads to ‘short circuit’.
Answer:
False. It leads to overloading. A short circuit happens when bare live and neutral wires touch each other.
In simple words: Too many devices cause overloading, not a short circuit.

Teacher's Note:
1. Both overload and short circuit give an excess current.
2. Fuses and MCBs protect against both.

Question 3. State whether the following statement is true or false.
‘Nichrome’ is the material used to make heating elements.
Answer:
True. Nichrome wire glows red hot without melting easily, so it is used in heaters and irons.
In simple words: Heaters use nichrome wire.

Teacher's Note:
1. Nichrome is an alloy with high resistance.
2. The heating coil is called the element.

Question 4. State whether the following statement is true or false.
Electric bell works on ‘heating effects of electric current’.
Answer:
False. The electric bell works on the magnetic effect of current, because its coil acts as an electromagnet.
In simple words: A bell uses an electromagnet.

Teacher's Note:
1. Heating effect is used in heaters and bulbs.
2. The hammer is pulled by the magnet.

Question 5. Fill in the blank.
Atom is considered neutral because it contains an equal number of _____ and ____ charges.
Answer:
positive and negative
In simple words: Equal positive and negative charges cancel out.

Teacher's Note:
1. Positive and negative charges balance in every atom.
2. Charging disturbs this balance.

Question 6. Fill in the blank.
________ is a major component of an electric bell.
Answer:
An electromagnet (coil on a soft iron core)
In simple words: The bell's coil acts as the magnet that pulls the hammer strip.

Teacher's Note:
1. The electromagnet is on only while current flows.
2. That on-off action makes the hammer vibrate.

Question 7. Fill in the blank.
Nichrome is the material used to make ________ elements.
Answer:
heating
In simple words: Nichrome is used for heating elements.

Teacher's Note:
1. It has a high melting point.
2. It is used in heaters, irons and toasters.

Question 8. Fill in the blank.
Materials that do not allow electric charges to flow through them are called ______.
Answer:
insulators
In simple words: Materials that block charge flow are insulators.

Teacher's Note:
1. Wood, plastic and air are insulators.
2. Insulation protects us from shocks.

Question 9. Fill in the blank.
Lightning is a natural phenomenon involving _______ particles.
Answer:
charged
In simple words: Lightning is the discharge of charge stored in clouds.

Teacher's Note:
1. The cloud collects charge that discharges through air.
2. Lightning conductors protect buildings.

Question 10. Fill in the blank.
In symbolic representation of an electric cell, the longer and shorter vertical lines represent _____ and _______ terminals, respectively.
Answer:
positive and negative
In simple words: The long thin line is + and the short thick line is −.

Teacher's Note:
1. The sign convention is the same in all circuit diagrams.
2. Look at the table of symbols in the Notes.

Question 11. Fill in the blank.
Mercury coated on zinc plate prevents the impurities from coming into contact with acid and prevents _______.
Answer:
local action
In simple words: Coating with mercury keeps impurities away from the acid.

Teacher's Note:
1. Local action wastes zinc.
2. This process is called amalgamation.

Question 12. Fill in the blank.
______ is a safety device that prevents excess flow of current through an appliance.
Answer:
Fuse
In simple words: A fuse breaks the circuit when too much current flows.

Teacher's Note:
1. It is placed in series with the appliance.
2. MCBs do the same job.

Question 13. Fill in the blank.
When bulbs are connected to the same source, the brightness of bulbs connected in parallel is _____ than the brightness of identical bulbs connected in series.
Answer:
more
In simple words: Parallel bulbs are brighter.

Teacher's Note:
1. Each bulb in parallel gets the full battery energy.
2. Series bulbs share the energy.

Question 14. Fill in the blank.
Electric heater works on the basis of ______ the electric current.
Answer:
heating effect of
In simple words: A heater turns electrical energy into heat.

Teacher's Note:
1. The coil of nichrome gets red hot.
2. Iron, toaster and kettle work the same way.

Teacher's Note:
1. The ammeter symbol has the letter A inside a circle.
2. A filament bulb glows because the wire heats up.

Teacher's Note:
1. The main fuse near the meter is sealed by the supply company.
2. Static electricity means charges that do not move.

Question 17. Identify whether the following circuits are open or closed.

Answer:
(a) Open circuit, because the key is not closed.
(b) Open circuit, because the bulb is fused.
(c) Open circuit, because silk is an insulator and cannot carry current.
(d) Closed circuit, as all the parts are joined by conducting wire and the switch is closed.
In simple words: A circuit is closed only when there is an unbroken path of conductors.

Teacher's Note:
1. Look for a gap, an open key, a fused bulb or an insulator in the path.
2. Copper, steel, silver and gold are conductors; silk is not.

Question 18. What are live and neutral wires?
Answer:
Electrical energy is supplied to houses through two wires, the live wire and the neutral wire. One end of an appliance is joined to the live wire and the other end to the neutral wire. Current flows from the live wire through the appliance to the neutral wire, and the electrical energy gets converted into other forms.
In simple words: These two wires bring the supply to the house and complete the path for the current.

Teacher's Note:
1. The switch and fuse are fitted on the live wire.
2. The live wire is the one that gives a shock when touched.