## Class 10 - Physics

**Question:**

(a) Why do electricians wear rubber hand gloves while working with electricity ?

(b) What p.d. is needed to send a current of 6 A through an electrical appliance having a resistance of 40 Î© ?

**Answer:**

(a) Electricians wear rubber hand gloves while working with electricity because rubber is an insulator and protects them from electric shocks.

(b) I=6amp, R=40ohm

We know that

V=IR

V = 6 x 40 = 240 V.

## Questions and Answers

**Electricity**- Questions

(a) How many milliamperes are there in 1 ampere ?

(b) How many microamperes are there in 1 ampere ?

Draw circuit symbols for (a) fixed resistance (b) variable resistance (c) a cell (d) a battery of three cells (e) an open switch (f) a closed switch.

What is a circuit diagram ? Draw the labelled diagram of an electric circuit comprising of a cell, a resistor, an ammeter, a voltmeter and a closed switch (or closed plug key). Which of the two has a large resistance : an ammeter or a voltmeter ?

State the factors on which the strength of electric current flowing in a given conductor depends.

Which has less electrical resistance : a thin wire or a thick wire (of the same length and same material) ?

Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?

A potential difference of 20 volts is applied across the ends of a resistance of 5 ohms. What current will flow in the resistance ?

Fill in the following blank with a suitable word :

Ohm’s law states a relation between potential difference and……………………

(a) Define the unit of resistance (or Define the unit “ohm”).

What happens to the resistance as the conductor is made thinner ?

Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change ?

The graph between V and 1 for a conductor is a straight line passing through the origin.

Which law is illustrated by such a graph ?

What should remain constant in a statement of this law ?

A p.d. of 10 V is needed to make a current of 0.02 A flow through a wire. What p.d. is needed to make a current of 250 mA flow through the same wire ?

A piece of wire of resistance 20 Î© is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.

The electrical resistivities of three materials P, Q and R are given below :

Which material will you use for making (a) electric wires (b) handle for soldering iron, and (c) solar cells ? Give reasons for your choices.

The electrical resistivities of five substances A, B, C, D and E are given below :

A 5.20 x l0^{-8} Î© m

If five resistances, each of value 0.2 ohm, are connected in series, what will be the resultant resistance ?

How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?

What possible values of resultant resistance one can get by combining two resistances, one of value 2 ohm and the other 6 ohm ?

Show how you would connect two 4 ohm resistors to produce a combined resistance of

(a) 2 ohms

(b) 8 ohms.

An electric bulb of resistance 20 Î© and a resistance wire of 4 Î© are connected in series with a 6 V battery. Draw the circuit diagram and calculate :

(a) total resistance of the circuit.

(b) current through the circuit.

(c) potential difference across the electric bulb.

(d) potential difference across the resistance wire.

For the circuit shown in the diagram below :

What is the value of :

(i) current through 6 Î©resistor ?

(ii) potential difference across 12 Î© resistor ?

Two resistors, with resistances 5 Î© and 10 Î© respectively are to be connected to a battery of emf 6 V so as to obtain :

(i) minimum current flowing (ii) maximum current flowing

(a) How will you connect the resistances in each case ? .

(b) Calculate the strength of the total current in the circuit in the two cases.

Which of the following are conductors and which are insulators ?

Sulphur, Silver, Copper, Cotton, Aluminium, Air, Nichrome, Graphite, Paper, Porcelain, Mercury, Mica, Bakelite, Polythene, Manganin.

(a) State the relation between potential difference, work done and charge moved.

(b) Calculate the work done in moving a charge of 4 coulombs from a point at 220 volts to another point at 230 volts.

(a) What do you understand by the term “potential difference” ?

(b) What is meant by saying that the potential difference between two points is 1 volt ?

(c) What is the potential difference between the terminals of a battery if 250 joules of work is required to transfer 20 coulombs of charge from one terminal of battery to the other ?

(d) What is a voltmeter ? How is a voltmeter connected in the circuit to measure the potential difference between two points. Explain with the help of a diagram.

(e) State whether a voltmeter has a high resistance or a low resistance. Give reason for your answer.

(a) In which direction does conventional current flow around a circuit ?

(b) In which direction do electrons flow ?

Which of the following equation shows the correct relationship between electrical units ?

1 A = 1 C/s or 1 C = 1 A/s

Fill in the following blanks with suitable words :

(a) A current is a flow of……….. For this to happen there must be a………….

(b) Current is measured in……… using an………… placed in……… in a circuit.

If the charge on an electron is 1.6 x 10^{-19} coulombs, how many electrons should pass through a conductor in 1 second to constitute 1 ampere current ?

An electric heater is connected to the 230 V mains supply. A current of 8 A flows through the heater.

(a) How much charge flows around the circuit each second ?

(b) How much energy is transferred to the heater each second ?

A resistance of 20 ohms has a current of 2 amperes flowing in it. What potential difference is there between its ends ?

A current of 5 amperes flows through a wire whose ends are at a potential difference of 3 volts. Calculate the resistance of the wire.

Classify the following into good conductors, resistors and insulators :

Rubber, Mercury, Nichrome, Polythene, Aluminium, Wood, Manganin, Bakelite, Iron, Paper, Thermocol, Metal coin

Fill in the following blanks with suitable words :

Resistance is measured in…………….. The resistance of a wire increases as the length…………………. ; as the

temperature………. ; and as the cross-sectional area…………

Will current flow more easily through a thick wire or a thin wire of the same material when connected to the same source ? Give reason for your answer.

How does the resistance of a conductor depend on :

(a) length of the conductor ?

(b) area of cross-section of the conductor ?

(c) temperature of the conductor ?

What would be the effect on the resistance of a metal wire of :

(a) increasing its length ?

(b) increasing its diameter ?

(c) increasing its temperature ?

How does the resistance of a wire change when :

(i) its length is tripled ?

(ii) its diameter is tripled ?

(in) its material is changed to one whose resistivity is three times ?

Calculate the area of cross-section of a wire if its length is 1.0 m, its resistance is 23 Î© and the resistivity of the material of the wire is 1.84 x 10^{-6} Î©m.

If 3 resistances of 3 ohm each are connected in parallel, what will be their total resistance ?

A wire that has resistance R is cut into two equal pieces. The two parts are joined in parallel. What is the resistance of the combination ?