Electricity

A student made an electric circuit shown here to measure the current through two lamps.
(a) Are the lamps in series or parallel ?
(b) The student has made a mistake in this circuit.
What is the mistake ?
(c) Draw a circuit diagram to show the correct way to connect the circuit.
Use the proper circuit symbols in your diagram.

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

Fill in the following blank with a suitable word :
Ohm’s law states a relation between potential difference and……………………

What is Ohm’s law ? Explain how it is used to define the unit of resistance.

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

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.

The electrical resistivities of four materials A, B, C and D are given below :

Which material is : (a) good conductor (b) resistor (c) insulator, and (d) semiconductor ?

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.

What is the SI unit of potential difference ?

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

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

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 ?

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.

Give the law of combination of resistances in series.

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 is the unit of electric charge ?

Which of the two is connected in series : ammeter or voltmeter ?

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 ?

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

On what factors does the resistance of a conductor depend ?

What is nichrome ? State its one use.

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

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 ?

The electrical resistivities of five substances A, B, C, D and E are given below :
A 5.20 x l0^-8 Ω m

Which of the following resistor arrangement, A or B, has the lower combined 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 ?

Calculate the combined resistance in each case :

A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω. How much current would flow through the 12 Ω resistor ?

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.

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

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

(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 ?

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

(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

What is the unit of electric current ?

What do the following symbols mean in circuit diagrams ?

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

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 ?

How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?

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

Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.

Name the material which is the best conductor of electricity.

Why are copper and aluminium wires usually used for electricity transmission ?

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

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…………

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 ?

How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?