Very Short Answer -Class 10 -Science- Physics-Chapter 12:Electricity

Class 10 -Science-Very Short Answer – Physics-Chapter 12:Electricity

Q1. (a).Name the instrument/device used to measure electric current in a circuit.

(b).How is an ammeter connected in a circuit to measure current flowing through it?

Ans :a. Ammeter is used to measure electric current.

b. Ammeter is connected in series in an electric circuit.

Q2.In an electric circuit, state the relationship between the direction of conventional current and the direction of flow of electrons.

Ans : Electrons flows from negative terminal to positive terminal where as current flows from +ve terminal to ve- terminal in external circuit i.e. Conventional current and electrons flow are opposite to each other.

 Q3. Define electric circuit. Distinguish between open and closed circuit.

Ans :Electric circuit is the arrangement in which electric current can flow when circuit is switched on. In open circuit there is no flow of current as the switch is off. In closed circuit a current flow in the circuit when switch is on.

Q4. Why is much less, heat generated in long electric cables than in filaments of electric bulbs?

 Ans : As heat produced IRt 2 = Electric cables are made of thick good conductor where as filaments are made of thin tungsten wire whose resistances is high. The resistance of electric cables is very less. So heat produced in cable is much lesser than filaments.

Q5. Name the device/instrument used to measure potential difference. How is it connected in an electric circuit?

Ans : The device which is used to measure potential difference is voltmeter. Voltmeter is connected in parallel in an electric circuit.

Q6. Define resistivity of a material.

We have R=p (l/A)

Resistivity p=R (A/l)

If A= 1, l=1, then P=R i.e. resistivity of a material is the resistance of a conductor of this material whose length and area of cross- section both are unity. or Resistivity of a material is the resistance of a conductor of this material whose volume is unity.

Q7. Give reason for the following:

a. Tungsten used almost exclusively for filament of electric lamp.

b. Why do we use copper and aluminium wires for transmission of electric current?

Ans : a. Tungsten is used in making the filament of electric lamp because it has high resistivity and high melting point.

b. The copper and aluminium have low resistivity and high conductivity.

Q8. State the factors on which the heat produced in a current carrying conductor depends. Give one practical application of this effect.

 Ans : We know that H = VIt  or H=I² Rt  Heat produced in a current carrying conductor

H∞ I² ? (Square of the current in the circuit)

∞ R ? (Resistance of the conductor)

∞ t ? (Time for which current is passed  in conductor) This effect applied in electric heater.

Q9. A large number of free electrons are present in metals yet no current flows in the absence of electric potential across it. Explain the statement with reason.

Ans :   Though there are large number of free electron present in a conductor, but their motion is random motion in the absence of potential difference. Their average velocity is zero. Hence there is no current flowing in conductor. But when a potential difference is applied across the ends of the conductor, it sets the electrons to move in a direction. The motion of charge produces an electric current in the conductor.

Q10. List in a tabular form two differences between a voltmeter and an ammeter.

Q11. Elements of electric toasters and electric iron are made of an alloy rather than a pure metal.

Give two reasons to justify the statement.

Ans :  a. Alloys have higher resistivity than their constituents pure metals.

 b. At high temperature alloys do not oxidise.

Q12. Why do the wires connecting an electric heater to the mains not glow while its heating element does?

Ans : Connecting wire has low resistivity or good conductivity, i.e. resistance of these wires is negligible hence no heat is produced while heating element is of an alloy whose resistivity is high, due to high resistance heat is produced in the element.

Q13. Give reason why tungsten is used for making filament of electric lamps. b. The elements of heating electrical appliances are made-up of an alloy rather than pure metal.

Ans : a. Due to (1) high resistivity and high melting point tungsten is used for making filaments of electric lamp.

b. high resistivity, and high melting point than their constituents’ pure metals which do not oxidise at high temperature.