Selina solutions for Concise Physics Class 10 ICSE chapter 8 - Current Electricity [Latest edition]

Define the term current and state its S.I unit. 

Define the term electric potential. State its S.I. unit.

How is the electric potential difference between the two points defined? State its S.I. unit.

Explain the statement ‘the potential difference between two points is 1 volt’.

State whether the current is a scalar or vector? What does the direction of current convey?

State whether the potential is a scalar or vector? What does the positive and negative sign of potential convey?

Name the particles which are responsible for the flow of current in a metallic wire.

Explain the flow of current in a metallic wire on the basis of movement of the particles named by you above in part.

What is the cause of resistance offered by the metallic wire in the flow of current through it?

State Ohm’s law and draw a neat labelled circuit diagram containing a battery, a key, a voltmeter, an ammeter, a rheostat and an unknown resistance to verify it. 

(a) Name and state the law which relates the potential difference and current in a conductor. 

(b) What is the necessary condition for a conductor to obey the law named above in part (a) ?

(a) draw a V-I graph for a conductor obeying Ohm’s law.

(b) what does the slope of V–I graph  for a conductor represent? 

Draw a I – V graph for a linear resistor. What does its slope represent? 

What is an ohmic resistor? Give one example of an ohmic resistor. Draw a graph to show its current voltage relationship. How is the resistance of the resistor determined from this graph?

What are non-ohmic reistors? Give one example and draw a graph to show its current-voltage relationship. 

Give two difference between an ohmic and non-ohmic resistor. 

Figure , below shows the I-V characteristic curves for four resistors. Identify the ohmic and non-ohmic resistors. Give a reason for your answer.  

Draw a V-I graph for a conductor at two different temperature. What conclusion do you draw from your graph for the variation of resistance of conductor with temperature?  

How does the resistance of a wire depend on its radius? Explain your answer. 

Two copper wires are of the same length, but one is thicker than the other.

1. Which wire will have more resistance?
2. Which wire will have more specific resistance?

How does the resistance of a wire depend on its length? Give a reason for your answer with reason. 

How does the resistance of a metallic wire depend on its temperature? Explain with reason. 

Two wires one of copper and other of iron, are of the same length and same radius. Which will have more resistance? Give reason. 

Name three factors on which resistance of a given wire depends and state how is it affected by the factors stated by you. 

Define the term resistivity and state its S.I unit. 

Write an expression connecting the resistance and resistivity. State the meaning of symbols used. 

State the order of resistivity of (i) a metal, (ii) a semiconductor and (iii) an insulator. 

Name two factors on which the specific resistance of a wire depends?

Two wires A and B are made of copper. The wire A is long and thin while the wire B is Short and thick. Which will have more specific resistance ?

Name a substance of which the resistance remains almost unchanged by the increase in  temperature. 

How does specific resistance of a semi-conductor change with the increase in temperature?

How does (a) resistance, and  (b) specific resistance of a wire depend on its (i) length, and (ii) radius?

Name the material used for making the connection wires. Give a reason for your answer. Why
should a connection wire be thick?

Name a material which is used for making the standard resistor. Give a reason for your answer.

Name the material used for making a fuse wire. Give a reason.

Name the material used for  filament of an electric bulb .

Name the material used for heating element of a room heater.

What is a superconductor? Give one example of it.

A substance has zero resistance below 1 k. what is such a substance called?

Which of the following is an ohmic resistance?

For which of the following substance, resistance decreases with increase in temperature?

In a conductor 6.25 × `10^16` electrons flow from its end A to B in 2 s. Find the current flowing
through the conductor (e = 1.6 × `10^19` C)

A current of 1.6 mA flows through a conductor. If charge on an electron is – 1.6 × `10^-19` coulomb,
find the number of electrons that will pass each second through the cross section of that
conductor.

Find the potential difference required to pass a current of 0.2 A in a wire of resistance 20Ω

An electric bulb draws 1.2 A current at 6.0 V. Find the resistance of filament of bulb while glowing.

A car bulb connected to a 12 volt battery draws 2 A current when glowing. What is the resistance of the filament of the bulb? Will the resistance be more same or less when the bulb is not glowing?

Calculate the current flowing through a wire of resistance 5 Ω connected to a battery of potential difference 3 V.

In an experiment of verification of Ohm’s law following observations are obtained.

Draw a characteristic V-I graph and use this graph to find:

1. potential difference V when the current I is 0.5 A,
2. current I when the potential difference V is 0.75 V,
3. resistance in a circuit.

Two wires of the same material and same length have radii r1 and r2 respectively compare: (i)
their resistances, (ii) their resistivities.

A given wire of resistance 1 Ω is stretched to double its length. What will be its new resistance?

A wire 3 ohm resistance and 10 cm length is stretched to 30 cm length. Assuming that it has a
uniform cross section, what will be its new resistance?

A wire of 9 ohm resistance having 30 cm length is tripled on itself. What is its new resistance? 

What length of copper wire of resistivity 1.7 × 10-8 𝛀 m and radius 1 mm is required so that its resistance is 1𝛀? 

The filament of a bulb takes a current 100 mA when potential difference across it is 0.2 V. When the potential difference across it becomes 1.0 V, the current becomes 400 mA. Calculate the resistance of filament in each case and account for the difference.

Explain the meaning of the terms e.m.f.., terminal voltage, and internal resistance of a cell.

State two differences between the e.m.f and terminal voltage of a cell. 

Name two factors on which the internal resistance of a cell depends and state how does it depend on the factors stated by you. 

A cell of e.m.f ε and internal resistance r is used to send current to an external resistance R. write expresssions for (a) the total resistance of circuit, (b) the current drawn from the cell. (c) the p.d
across the cell. And (d) voltage drop inside the cell. 

A cell is used to send current to an external circuit. (a) How does the voltage across its terminals compare with its e.m.f? (b) under what condition is the e.m.f of a cell equal to its terminal
voltage? 

Explain why the p.d across the terminals of a cell is more in an open circuit and reduced in a closed circuit. 

Write the expressions for the equivalent resistance R of three resistors R1, R2 and R3 joined in
(a) parallel (b) series 

How would you connect two resistors in series? Draw a diagram. Calculate the total equivalent resistance.  

Show by a diagram how two resistors R1 and R2 are joined in parallel. Obtain an expression for the total resistance of combination. 

State how are the two resistors joined with a battery in each of the following cases when: 

same current flows in each resistor 

State how are the two resistors joined with a battery in each of the following cases when: 

potential difference is same across each resistor 

State how are the two resistors joined with a battery in each of the following cases when:  

equivalent resistance is less than either of the two resistances 

State how are the two resistors joined with a battery in each of the following cases when: 

equivalent resistance is more than either of the two resistances. 

The V-I graph for a series combination and for a parallel combination of two resistors is shown in Fig – 8.38. Which of the two, A or B, represents the parallel combination? Give a reason for your answer. 

In series combination of resistances:

In parallel combination of resistances:

Which of the following combinations have the same equivalent resistance between X and Y?  

The diagram below in Fig. 8.40 shows a cell of e.m.f. ε = 2 volt and internal resistance r = 1 ohm to an external resistance R = 4 ohm. The ammeter A measures the current in the circuit and the
voltmeter V measures the terminal voltage across the cell. What will be the readings of the ammeter and voltmeter when (i) the key K is open, (ii) the key K is closed. 

A battery of e.m.f 3.0 V supplies current through a circuit in which the resistance can be changed.
A high resistance voltmeter is connected across the battery. When the current is 1.5 A, the voltmeter reads 2.7 V. Find the internal resistance of the battery. 

A cell of e.m.f. 1.8V and internal resistance 2Ω is connected in series with an ammeter of resistance 0.7Ω and a resistor of 4.5Ω as shown in Fig. 8.41 

(a) what would be the reading of the ammeter?
(b) what is the potential difference across the terminals of the cell? 

A battery of e.m.f. 15 V and internal resistance 3 ohm is connected to two resistors of resistances 3 ohm and 6 ohm is series Find:
(a) the current through the battery
(b) the p.d. between the terminals of the battery. 

A cell of e.m.f. ε and internal resistance 𝔯 sends current 1.0 A when it is connected to an external resistance 1.9Ω. But it sends current 0.5 A when it is connected to an external resistance 3.9 Ω.
Calculate the values of ε and 𝔯.

Two resistors having resistance 4𝛀 and 6𝛀 are connected in parallel. Find their equivalent resistance. 

Four resistors each of resistance 2Ω are connected in parallel. What is the effective resistance? 

You have three resistors of values 2Ω, 3Ω and 5Ω. How will you join them so that the total  resistance is less than 1Ω? Draw diagram and find the total resistance. 

Three resistors each of 2Ω are connected together so that their total resistance is 3Ω. Draw a diagram to show this arrangement and check it by calculation. 

Calculate the equivalent resistance of the following combination of resistors r1, r2, r3 and r4 if `r_1=r_2=r_3=r_4=2.0Ω ` between the points A and B in Fig. 8.42  

A combination consists of three resistors in series. Four similar sets are connected in parallel. If the resistance of each resistor is 2 ohm, find the resistance of the combination. 

In the circuit shown below in Fid 8.43, calculate the value of x if the equivalent resistance between A and B is 4Ω.  

Calculate the effective resistance between the points A and B in the circuit shown in Figure 8.44.  

A wire of uniform thickness with a resistance of 27Ω is cut into three equal pieces and they are joined in parallel. Find the equivalent resistance of the parallel combination. 

A circuit consists of a 1 ohm resistor in series with a parallel arrangement of 6 ohm and 3 ohm resistors. Calculate the total resistance if the circuit. Draw a diagram. 

Calculate the effective resistance between the points A and B in the network shown below in figure.

Calculate the equivalent resistance between A and B in the adjacent diagram.

In the network shown in the following adjacent Figure, calculate the equivalent resistance between the points.  

1. A and B
2. A and C

Five resistors, each 3 Ω, are connected as shown in Fig 8.48. Calculate the resistance (a) between the points P and Q. (b) between the points X and Y.  

Two resistors of 2.0 Ω and 3.0 Ω are connected (a) in series (b) in parallel, with a battery of 6.0 V and negligible internal resistance. For each case draw a circuit diagram and calculate the current through the battery. 

A resistor of 6Ω is connected in series with another resistor of 4 Ω. A potential difference of 20 V is applied across the combination. Calculate (a) the current in the circuit and (b) the potential difference across the 6Ω resistor. 

Two resistors of resistance 4 Ω and 6 Ω are connected in parallel to a cell to draw 0.5 A current from the cell.

Draw a labeled diagram of the arrangement

Two resistors of resistance 4 Ω and 6 Ω are connected in parallel to a cell to draw 0.5 A current from the cell.

Calculate current in each resistor. 

Calculate current flowing through each of the resistors A and B in the circuit shown in following figure?

In the following figure calculate:

1. the total resistance of the circuit
2. the value if R, and
3. the current flowing in R.

A particular resistance wire has a resistance of 3 ohm per meter. Find:
The total resistance of three lengths of this wire each 1.5 m long, joined in parallel.

A particular resistance wire has a resistance of 3 ohm per meter. Find :

The potential difference of the battery which gives a current of 2 A in each of the 1.5 m length when connected in the parallel to the battery (assume that resistance of the battery is negligible).

A particular resistance wire has a resistance of 3 ohm per meter. Find :

The total resistance of three lengths of this wire each 1.5 m long, in parallel.

A cell supplies a current of 1.2 A through two 2 Ω resistors connected in parallel. When the resistors are connected in series, it supplies a current of 0.4 A. Calculate: (i) the internal resistance and (ii) e.m.f. of the cell. 

A battery of e.m.f 15 V and internal resistance 3 Ω is connected to two resistors 3Ω and 6Ω connected in parallel. Find: (a) the current through the battery. (b) p.d. between the terminals of the battery, (c) the current in 3 Ω resistors, (d) the current in 6 Ω resistor. 

The following circuit diagram shows three resistors 2 Ω, 4 Ω and R Ω connected to a battery of e.m.f 2V and internal resistance 3 Ω. If the main current of 0.25 A flows through the circuit, find:

1. the p.d. across the 4 Ω resistors,
2. the p.d. across the internal resistance of the cell,
3. the p.d. across the R Ω or 2 Ω resistors, and
4. the value of R.

Three resistors of 6.0 ohm, 2.0 ohm and 4.0 ohm are joined to ammeter A and a cell of emf 6.0 V as shown in following figure. Calculate :

(a) the efective resistance of the circuit.

(b) the reading of ammeter

The following diagram shows the arrangement of five different resistances connected to a battery of e.m.f. 1.8V Calculate:
(a) the total resistance of the circuit, and
(b) the reading of ammeter A. 

A cell of e.m.f. 2 V and internal resistance 1.2 Ω is connected to an ammeter of resistance 0.8 Ω and two resistors of 4.5 Ω and 9 Ω as shown in following figure.

Find:

1. The reading of the ammeter,
2. The potential difference across the terminals of the cells, and
3. The potential difference across the 4.5 Ω resistor.

Write an expression for the electrical energy spent in flow of current through an electrical appliance in terms of current, resistance and time.

Write an expression for the electrical power spent in flow of current through a conductor in terms of resistance and potential difference.

Write an expression for the electrical power spent in flow of current through a conductor in terms of  current and resistance.

Electrical power P is given by the expression P = (Q × V) ÷ time

(a) What do the symbols Q and V represent?

(b) Express the power P in terms of current and resistance explaining the meanings of symbols used there in.

Name the S.I. unit of electrical energy. How is it related to Wh?

Explain the meaning of the statement 'the power of an appliance is 100 W'.

State the S.I. units of electrical power.

State and define the household unit of electricity.

What is the voltage of the electricity that is generally supplied to a house?

What is consumed while using different electrical appliances, for which electricity bills are paid? 

Name the physical quantity which is measured in (i) kW, (ii) kWh.

Define the term kilowatt - hour and state its value in S.I. unit.

How do kilowatt and kilowatt-hour differ ?

Complete the following:

1 kWh = `(1 "volt" xx 1 "ampere" xx "_________")/1000`

Complete the following:

1 kWh = _________ J

What do you mean by power rating of an electrical appliance? How do you use it to calculate 

(a) the resistance of the appliance and

(b) the safe limit of the current in it, while in use?

An electric bulb is marked '100 W, 250 V'. What information does this convey?

List the names of three electrical gadgets used in your house. Write their power, voltage rating and approximate time for which each one is used in a day. Hence find the electrical energy consumed by each in day.

Twolamps, one rated 220 V, 50 W and the other rated 220 V, 100 W, are connected in series with mains of 220 V. Explain why does the 50 W lamp consume more power.

Name the factors on which the heat produced in a wire depends when current is passed in it, and state how does it depend on the factors stated by you.

When a current I flows through a resistance R for time t, the electrical energy spent is given by : 

An electrical appliance has a rating 100 W, 120V. The resistance of element of appliance when in use:

An electric bulb of resistance 500 Ω draws current 0.4 A from the source. Calculate:
(a) the power of bulb and
(b) the potential difference at its end.

A current of 2 A is passed through a coil of resistance 75 Ω for 2 minutes.
(a) How much heat energy is produced?
(b) How much charge is passed through the resistance?

Calculate the current through a 60 W lamp rated 250 V. If the line voltage falls to 200 V, how is power consumed by the bulb affected?

An electric bulb is rated '100 W, 250 V'. How much current will the bulb draw if connected to a 250 V supply ?

An electric bulb is rated at 220 V, 100 W.
(a) What is its resistance?
(b) What safe current can be passed through it?

A bulb of 40 W is used for 12.5 h each day for 30 days. Calculate the electrical energy consumed.

An electric iron is rated 750 W, 230 V. Calculate the electrical energy consumed by the iron in 16 hours.

An electrical appliance having a resistance of 200 Ω  is operated at 220 V. calculate the energy consumed by the appliance in 5 minutes.
in joules.

An electrical appliance having a resistance of 200 Ω is operated at 220 V. calculate the energy consumed by the appliance in 5 minutes in kWh.

A bulb marked 12 V, 24 W operates on a 12 V battery for 20 minutes. Calculate:

(i) The current flowing through it, and

(ii) The energy consumed.

A current of 0.2 A flows through a wire whose ends are at a potential difference of 15 V. Calculate:

(i) The resistance of the wire, and

(ii) The heat energy produced in 1 minute.

What is the resistance, under normal working conditions, of an electric lamp rated at '240 v, 60 W' ? If two such lamps are connected in series across a 240 V mains supply, explain why each one appears less bright.

Two bulbs are rated 60 W, 220 V and 60 W, 110 V respectively. Calculate the ratio of their resistances.

An electric bulb is rated 250 W, 230 V. 

(i) the energy consumed in one hour, and

(ii) the time in which the bulb will consume 1.0 kWh energy when connected to 230 V mains.

Three heaters each rated 250 W, 100 V are connected in parallel to a 100 V supply. Calculate :

The total current taken from the supply

Three heaters each rated 250 W, 100 V are connected in parallel to a 100 V supply. The resistance of each heater

Three heaters each rated 250 W, 100 V are connected in parallel to a 100 V supply of the energy supplied in kWh to the three heaters in 5 hours.

A bulb is connected to a battery of p.d. 4 V and internal resistance 2.5 Ω . A steady current of 0.5 A flows through the circuit. Calculate:

The total energy supplied by the battery in 10 minutes

A bulb is connected to a battery of p.d. 4 V and internal resistance 2.5 Ω . A steady current of 0.5 A flows through the circuit. Calculate:

The resistance of the bulb

A bulb is connected to a battery of p.d. 4 V and internal resistance 2.5 Ω . A steady current of 0.5 A flows through the circuit. Calculate:

The energy dissipated in the bulb in 10 minutes.

Two resistors A and B of 4 Ω and 6 Ω  respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate: the power supplied by the battery .

Two resistors A and B of 4 Ω and 6 Ω respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate : 

the power dissipated in each resistor.

A battery of e.m.f. 15 V and internal resistance 2 Ω   is connected to two resistors of resistances 4 ohm and 6 ohm joined (a) in series. Find in each case the electrical energy spent per minute in 6 Ω resistor.

Water in an electric kettle connected to a 220 V supply took 5 minutes to reach its boiling point. How long would it have taken if the supply had been of 200 V?

An electric toaster draws 8 A current in a 220 V circuit. It is used for 2 hr. Find the cost of operating the toaster if the cost of electrical energy is Rs. 4.50 per kWh.

An electric kettle is rated 2.5 kW, 250 V. Find the cost of running the kettle for two hours at Rs. 5.40 per unit.

A geyser is rated 1500 W, 250 V. This geyser is connected to 250 V mains. Calculate:

(i) The current drawn,

(ii) The energy consumed in 50 hours, and

(iii) The cost of energy consumed at Rs 4.20 per kWh.