#### Question: Mention one reason why tungsten is used for making filament of electric lamp.

**Answer:** It has low resistivity and high melting point.

#### Question: Calculate the number of electrons constituting one coulomb of change.

(Charge one electron = 1.6 × 10^{-19}C)

**Answer: **Number of electron = 1C/1.6 × 10^{-19}C

= 0.625 × 10^{19}

= 6.25 × 10^{-18}

#### Question: (i) Name the instrument / device used to measure electric current in a circuit.

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

**Answer:** (i) Ammeter (ii) In series

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

**Answer:** The direction of conventional current is opposite to the direction of flow of electrons.

#### Question: How does the resistivity of alloys compare with those of pure metals from which they may have been formed?

**Answer:** Alloys have higher resistivity in comparison to pure metals.

#### Question: Write SI unit of resistivity.

**Answer:** Ohm-metre (Ω m).

#### Question: State a difference between the wire used in the element of an electric heater and in a wire.

**Answer:** The wire used in the element of an electric heater has very high resistance while that in a fuse wire has a low resistance.

#### Question: Power of a lamp is 60 W. Find the energy in joules consumed by it in 1 s.

**Answer: **Energy consumed = P**×**t = 60**×**1 = 60 J

#### Question: Which particles are responsible for the flow of current in conductors?

**Answer:** Electrons

#### Question: Define electrostatic potential at a point.

**Answer:** Electric potential at a point is defined as the amount of work done in moving a unit charge from infinity to that point.

#### Question: What is the SI unit of electric potential?

**Answer:** In SI, electric potential is measured in volt (V).

#### Question: Write the mathematical expression for electric potential.

**Answer:** Mathematically, electric potential is written as V = W/q.

#### Question: Is electrostatic potential a scalar quantity or a vector quantity?

**Answer:** It is a scalar quantity.

#### Question: What is potential difference? Is it a scalar quantity or a vector quantity? Give its SI units.

**Answer:** It is the amount of work done in moving a unit charge between two given points. It is a scalar quantity and is measured in volt.

#### Question: When is potential different between two points said to be 1 volt?

**Answer:** Potential difference between two points is said to be one volt, if a work of 1 joule is done to move a charge of 1 coulomb between the two points.

#### Question: How can we maintain a potential difference across a conductor?

**Answer:** By using a source of emf. For example, a battery.

#### Question: Give a single word for 1 joule/1 coulomb.

**Answer:** 1 volt

#### Question: How many joule are there in one kilowatt hour?

**Answer: **3.6 × 10^{6 }J

#### Question: How can we measure the potential different across the end of a conductor?

**Answer:** By using a device called voltmeter.

#### Question: How can measure the current in a circuit?

**Answer: **By using s device called an ammeter.

#### Question: How does the resistance of a wire vary with its cross-sectional area?

**Answer:** It varies inversely with the cross-sectional area.

#### Question: How is voltmeter connected in a circuit?

**Answer:** It is always connected in parallel in a circuit.

#### Question: How is an ammeter connected in a circuit?

**Answer:** It is always connected in series in a circuit.

#### Question: Define current. Give its SI unit.

**Answer:** Current is defined as the rate of flow electrons. It is measured in ampere (A).