Physics

Electricity

Question:

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

Answer:

Potential difference, V = 20V
Resistance, R = 5ohms
Current, I = ?
We know that
V=IR
20 = I x 5
I = 20/5 = 4 A

 

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Electricity

Q 1.

Compare how an ammeter and a voltmeter are connected in a circuit.

Q 2.

What is an ammeter ? How is it connected in a circuit ? Draw a diagram to illustrate your answer.

Q 3.

Which among iron and mercury is a better conductor of electricity ?

Q 4.

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 ?

Q 5.

What is the unit of electric charge ?

Q 6.

A current of 4 A flows around a circuit for 10 s. How much charge flows past a point in the circuit in this time ?

Q 7.

Name the material which is the best conductor of electricity.

Q 8.

Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change ?

Q 9.

Draw a circuit diagram to show how 3 bulbs can be lit from a battery so that 2 bulbs are controlled by the same switch while the third bulb has its own switch.

Q 10.

Name the material which is used for making the heating element of an electric iron.

Q 11.

Which of the following statements correctly defines a volt ?
(a) a volt is a joule per ampere.
(b) a volt is a joule per coulomb.

Q 12.

By what name is the physical quantity coulomb/second called ?

Q 13.

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

Q 14.

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…………

Q 15.

Find the current in each resistor in the circuit shown below :
lakhmir-singh-physics-class-10-solutions-electricity-38(12)

Q 16.

(a) What do the letters p.d. stand for ?
(b) Which device is used to measure p.d. ?

Q 17.

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 ?

Q 18.

(a) Name a device that helps to measure the potential difference across a conductor.
(b) How much energy is transferred by a 12 V power supply to each coulomb of charge which it moves around a circuit ?

Q 19.

Name the law which relates the current in a conductor to the potential difference across its ends.

Q 20.

On what factors does the resistance of a conductor depend ?

Q 21.

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 ?

Q 22.

The electrical resistivities of four materials A, B, C and D are given below :
Untitled
Which material is : (a) good conductor (b) resistor (c) insulator, and (d) semiconductor ?

Q 23.

Give the law of combination of resistances in series.

Q 24.

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

Q 25.

Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.

Q 26.

What is the SI unit of potential difference ?

Q 27.

What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.

Q 28.

What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?

Q 29.

What actually travels through the wires when you switch on a light ?

Q 30.

What do the following symbols mean in circuit diagrams ?
lakhmir-singh-physics-class-10-solutions-electricity-1

Q 31.

If 20 C of charge pass a point in a circuit in 1 s, what current is flowing ?

Q 32.

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.

Q 33.

(a) Name a device which helps to maintain potential difference across a conductor (say, a bulb).
If a potential difference of 10 V causes a current of 2 A to flow for 1 minute, how much energy is
transferred ?

Q 34.

(a) What is an electric current ? What makes an electric current flow in a wire ?
(b) Define the unit of electric current (or Define ampere).

Q 35.

Name the unit of electrical resistance and give its symbol.

Q 36.

(a) What is the ratio of potential difference and current known as ?
(b) The values of potential difference V applied across a resistor and the corresponding values of current I
flowing in the resistor are given below :
lakhmir-singh-physics-class-10-solutions-electricity-4
(c) Name the law which is illustrated by the above V-I graph.
(d) Write down the formula which states the relation between potential difference, current and resistance,
(e) The potential difference between the terminals of an electric iron is 240 V and the current is 5.0 A. What is the resistance of the electric iron ?

Q 37.

A current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor ?

Q 38.

Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.

Q 39.

Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?

Q 40.

(a) Write down an expression for the resistance of a metallic wire in terms of the resistivity.
What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 × 10-6 m2, if the resistivity of the metal be 2.8 × 10-8 Ωm ?

Q 41.

(a) Give two examples of substances which are good conductors of electricity. Why do you think they are
good conductors of electricity ?
Calculate the resistance of a copper wire 1.0 km long and 0.50 mm diameter if the resistivity of copper is 1.7 × 10-8 Ωm.

Q 42.

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 ?

Q 43.

(a) Define resistivity. Write an expression for the resistivity of a substance. Give the meaning of each symbol
which occurs in it.
(b) State the SI unit of resistivity.
(c) Distinguish between resistance and resistivity.
(d) Name two factors on which the resistivity of a substance depends and two factors on which it does not depend.
(e) The resistance of a metal wire of length 1 m is 26 Ω at 20 °C. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature ?

Q 44.

The electrical resistivities of three materials P, Q and R are given below :
Untitled
Which material will you use for making (a) electric wires (b) handle for soldering iron, and (c) solar cells ? Give reasons for your choices.

Q 45.

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

Q 46.

State the law of combination of resistances in parallel.

Q 47.

An electric bulb of resistance 20 Ω and a resistance wire of 4 Ω 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.

Q 48.

Two resistors, with resistances 5 Ω and 10 Ω 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.

Q 49.

The circuit diagram given below shows the combination of three resistors R1 R2 and R3 :
lakhmir-singh-physics-class-10-solutions-electricity-39(19)
Find : (i) total resistance of the circuit.
(ii) total current flowing in the circuit.
(iii) the potential difference across R1.

Q 50.

How much work is done when one coulomb charge moves against a potential difference of 1 volt ?