Class 10-Science ch-12 Electricity

What does an electric circuit mean?

Define the unit of electric current.

Calculate the number of electrons constituting one coulomb of charge.

Name a device that helps to maintain a potential difference across a conductor.

What is meant by saying that the potential difference between two points is 1 V?

How much energy is given to each coulomb of charge passing through a 6 V battery?

On what factors does the resistance of a conductor depend?

Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? why?

Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

10.

Why are coils of electric toasters and electric irons made of alloys rather than pure metal?

11.

Use the given table to answer the questions.

(i) Which among iron and mercury is a better conductor?
(ii) Which material is the best conductor?

12.

Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, three resistors of 5 $Ω$ , 8 $Ω$ and 12 $Ω$ and a plug key, all connected in series.

13.

Redraw the above circuit, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across 12 $Ω$ resistor. What would be the reading in ammeter and voltmeter?

14.

Judge the equivalent resistance when the following are connected in parallel
(i) $1 Ω a n d 10^{6} Ω$
(ii) $1 Ω, 10^{3} Ω a n d 10^{6} Ω$

15.

An electric lamp of 100 $Ω$ , toaster of 50 $Ω$ and a water filter of resistance 500 $Ω$ are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all the three appliances and what is the current through it?

16.

What are advantages of connecting electrical appliances in parallel with the battery instead of connecting them in series?

17.

How can three resistors of resistances 2 $Ω$ , 3 $Ω$ , and 6 $Ω$ be are connected to give a total resistance of
(i) 4 $Ω$
(ii) 1 $Ω$

18.

What is (i) the highest and (ii) the lowest total resistance which can be secured by combinations of four coils of resistance 4 $Ω$ , 8 $Ω$ , 12 $Ω$ and 24 $Ω$ ?

19.

Why does the cord of an electric heater not glow while heating element does?

20.

Compute the heat generated while transferring 96000 C of charge in one hour through a potential difference of 50 V?

21.

An electric iron of resistance 20 $Ω$ takes a current 5 A. Calculate the heat developed in 30 s.

22.

What determines the rate at which energy is delivered by a current?

23.

An electric motor takes 5 A from a 220 V line. Determine the power of the motor energy consumed in 2 h.

24.

A piece of wire of resistance R is cut into five equal parts. These parts are connected in parallel. If equivalent resistance of this combination is R', then find the ratio R/R'
(1) $\frac{1}{25}$
(2) $\frac{1}{5}$
(3) 5
(4) 25

25.

Which of the following terms does not represent electric power in a circuit?
(1) $I^{2} R$
(2) $I R^{2}$
(3) VI
(4) $V^{2} / R$

26.

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, then the power consumed will be
(1) 100 W
(2) 75 W
(3) 50 W
(4) 25 W

27.

Two conducting wires of same material and of equal lengths and equal diameter are first connected in series and there parallel in a circuit across the same potential difference, the ratio of heat produced in series and parallel combinations would be
(1) 1:2
(2) 2:1
(3) 1:4
(4) 4:1

28.

How is voltmeter connected in circuit to measure the potential difference between the two points?

29.

A copper wire has diameter 0.5 mm and resistivity $ρ = 1.6 \times 10^{- 8} Ω m .$ What will be the length of its wire to make its resistance 10 $Ω$ ? How much does the resistance change, if diameter is doubled?

30.

The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are as given below:
$\begin{matrix} I (a m p e r e s) & 0.5 & 1.0 & 2.0 & 3.0 & 4.0 \\ V (v o l t s) & 1.6 & 3.4 & 6.7 & 10.2 & 13.2 \end{matrix}$
Plot a graph between V and I and also calculate the resistance of that resistor.

31.

When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the current. Find the value of resistance of the resistor.

32.

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 $Ω$ , respectively. How much current would flow through the 12 $Ω$ resistor?

33.

How many 176 $Ω$ resistors (in parallel) are required to carry 5 A on a 220 V line?

34.

Show how would you connect three resistors, each of resistance 6 $Ω$ , so that the combination has a resistance of (i) 9 $Ω$ and (ii) 4 $Ω$ ?

35.

Several electric bulbs designed to be used on a 220 V electric supply line is rated at 10 W. How many lamps are connected in parallel with each other across two wires 220 V line if the maximum allowable current is 5 A?

36.

A hot late of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 $Ω$ resistance, which may be used separately in series or in parallel. What are the currents in three cases?

37.

Compare the power used in 2 $Ω$ resistors in each of the following circuits (i) a 6 V battery in series with 1 $Ω$ and 2 $Ω$ resistors. (ii) a 4 V battery in parallel with 12 $Ω$ and 2 $Ω$ resistors.

38.

Two lamps, one rated at 100 W-220 V and other 60 W - 220 V are connected in parallel to the electric mains supply. What current is drawn from the line, if the supply voltage is 220 V?

39.

Which uses more energy, a 250 W TV set in 1 h or a 1200 W toaster in 10 min?

40.

An electric heater of resistance 8 $Ω$ draws 15 A from the mains for 2 h. Calculate the rate at which heat is developed in the heater.

41.

Explain the following questions
(i) Why is tungsten used almost exclusively for filament of electric lamps?
(ii) Why are the conductors of electric heating devices such as bread toaster and electric irons made of alloys rather than pure metals?
(iii) Why are copper and aluminium wires usually employed for electricity transmission?
(iv) How does the resistance of a wire vary with its area of cross-section?
(v) Why are copper and aluminium wires usually employed for electricity transmission?

42.

What causes the potential difference between the two terminals of a cell?

43.

Write one function of the given symbol.

44.

Draw a circuit diagram using a cell of two batteries, two resistors of 3 $Ω$ each connected in series, a plug key and a rheostat.

45.

Why closed path is required for the flow of current?

46.

When two ends of a metallic wire are connected across the terminals of a cell, then some potential difference is set up between its ends. In which direction electrons are flowing through the conductors?

47.

Draw the V-I graph for ohmic and non-ohmic conductors.

48.

Out of the two wires P and Q shown as alongside, which one has greater resistance? Justify about it.

49.

The voltage-current (V-I) graph of a metallic circuit at two different temperatures $T_{1} a n d T_{2}$ is shown in the figure. Which of the two temperatures is higher and why?

50.

Find the minimum resistance that can be made using five resistors each of 1/5 $Ω$ .

51.

What is the resistance of air gap?

52.

You have two metallic wires of resistances 3 $Ω$ . How will you connect these wires to get the effective resistance of 2 $Ω$ .

53.

The given figure shows three resistors.

Find the combined resistance.

54.

A wire of resistivity $ρ$ is pulled to double its length. What will be its new resistivity?

55.

A student using the same two resistors, ammeter, voltmeter, and battery, makes two circuits connecting the two resistors first in series and other in parallel. If the ammeter and voltmeter readings in both the cases are respectively. Write his observations.

56.

How does the resistance of an ohmic conductor depend on the applied voltage?

57.

The resistance of a resistor is kept constant and the potential difference across its two ends is decreased to half of its former value. State the change that will occur in the current flowing through it.

58.

What happens to the other bulbs in a series circuit, if one bulb blows off?

59.

Write the relation between heat energy produced in a conductor when a potential difference V is an applied across its terminals and a current I flows through it for time t.

60.

Give two examples for the application of the heating effect of electric current.

61.

Nichrome is used to make the element of an electric heater. Why?

62.

Name and define the smallest commercial unit of electricity.

63.

The resistance of an incandescent filament of a bulb is comparatively much more than that when it is at room temperature. Why?

64.

What do you understand by the term fuse in an electric circuit?

65.

In how much time will a bulb of 100 W consume the energy of 2 kWh?

66.

(i) What are the values of mA and $μ A$ ?
(ii) Draw the symbols of battery and rheostat.

67.

A current of 1 A is drawn by a filament of an electric bulb. What would be the number of electrons passing through a cross-section of the filament in 16s?

68.

Derive an expression for equivalent resistance in the following case.

Decide which resistances are in series and parallel. Solve for series and then for parallel. Combine both the results to get the equivalent resistance.

69.

Find the equivalent resistance in the following circuit.

70.

An electrician puts a fuse of rating 5 A in that part of the domestic electrical circuit in which an electric heater of rating 1.5 kW, 220 V is operating. What is likely to happen in this case and why?

71.

In an electrical circuit, two resistors of 2 $Ω$ and 4 $Ω$ are connected in series to a 6 V battery. Find the heat dissipated by the 4 $Ω$ resistors in 5 s.

72.

320 J of heat is produced in 10 s in a 2 $Ω$ resistor. Find the amount of current flowing through the resistor.

73.

Three 2 $Ω$ resistors, A, B, and C are connected as shown in the figure. Earth of them dissipates energy and can withstand a maximum power of 18 W without melting. Find the maximum current that can flow through the three resistors?

74.

If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), then find the increase in power dissipated.

75.

n resistors, each of resistance R is first connected in series and then in parallel. what is the ratio of the total in parallel? What is the ratio of the total effective resistance of the circuit in series to the parallel combination?

76.

Should the resistance of an ammeter be low or high? Give reason.

77.

In an electrical circuit, three incandescent bulbs A, B and C of rating 40 W, 60W and 100 W respectively, are connected in parallel to an electric source. Write the order of brightness.

78.

What is meant by electric current? Write its SI unit. Calculate the amount of charge that flows through a conductor when a current of 5 A flows through it for 2 min.

79.

(i) State the relation between potential difference, work done and charge moved.
(ii) Calculate the work done in moving a charge of 4 C from a point at 220 V to a point at 230 V.

80.

Study the following circuit and answer the questions that follow:

(i) State the type of combination of two resistors in the circuit.
(ii) How much current is flowing through
(a) 10 $Ω$
(b) 15 $Ω$ resistor?
(iii) What is the ammeter reading?

81.

Five resistors are connected in a circuit as shown in the figure. Find the ammeter reading when the circuit is closed.

82.

Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 $Ω$ in series with a combination of two resistors (4 $Ω$ each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2 $Ω$ resistor be the same as that across the parallel combination of 4 V resistors? Give reasons.

83.

A circuit diagram is given as shown below:

Calculate
(i) The total effective resistance of the circuit.
(ii) The total current in the circuit.
(iii) The current through each resistor.

84.

Read the following informations:
(i) Resistivity of copper is lower than that of aluminium which in turn is lower than that of constantan.
(ii) Six wire labelled as A, B, C, D, E and F have been designed as per the following parameters:

Answer the following questions using the above data:
(a) which of the wires has maximum resistance and why?
(b) Which of the wires has minimum resistance and why?
(c) Arrange $R_{1}, R_{3} a n d R_{5}$ in ascending order of their values. Justify your answer.

85.

What is meant by the "electrical resistance" of a conductor? State how the resistance of a conductor is affected when (i) a low current passes through it for a short duration, (ii) a heavy current passes through it for about 30 s.

86.

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) (a) minimum current
(b) maximum current
(ii) How will you connect the resistances in each case?
(iii) Calculate the strength of the total current in the circuit in the two cases.

87.

A metal wire has diameter of 0.25 mm and electrical resistivity of $0.8 \times 10^{- 8} Ω - m$ .
(i) What will be the length of this wire to make a resistance 5 $Ω$
(ii) How much will the resistance change, if the diameter of the wire is doubled?

88.

A battery E is connected to three identical lamps P, Q and R as shown in figure. Initially, the switch S is kept open and the lamp P and Q are observed to glow with same brightness. Then, switch S is closed.

How will the brightness of glow of bulbs P and Q will change? Justify your answer.

89.

You have two electric lamps having rating 40 W, 220 V and 60 W, 220 V. Which of the two has a higher resistance? Give reason for your answer. If these two lamps are connected to a source of 220 V, which will glow brighter?

90.

The potential difference between two terminals of an electric iron is 220 V and the current flowing through its element is 5 A. Calculate the resistance and wattage of the electric iron.

91.

An electric heater is rated at 2 kW. Calculate the cost of using it for 2 h daily for the month of September, if each unit costs Rs 4.

92.

An electric geyser rated at 1500 W, 250 V is connected to a 250 V line mains. Solve
(i) the electric current drawn by it.
(ii) energy consumed by it in 50 h.
(iii) cost of energy consumed if each unit costs Rs 6

93.

Three 2 $Ω$ resistors, A, B, and C are connected as shown in the figure. Each of them dissipates energy and can withstand a maximum power of 18 W without melting. Find the maximum current that can flow through the three resistors.

94.

An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum rate. The applied voltage is 220 V. What is the value of current and the resistance in each case?

95.

An electrical bulb is rated 40 W, 220 V. How many bulbs can be connected in parallel with each other across the two wires of 220 V line, if the maximum allowable current is 6 A?

96.

A heater coil connected to 200 V has a resistance of 80 $Ω$ . If the heater is plugged in for the time t such that 1 kg of water at $20 ° C$ attains a temperature of $60 ° C$ . Find
(i) the power of heater
(ii) the heat absorbed by water
(iii) the value of t in seconds

97.

(i) Distinguish between the terms electrical resistance and resistivity of conductor.
(ii) A copper wire of resistivity $1.63 \times 10^{- 8} Ω - m$ has cross-section area of $10.3 \times 10^{- 4} c m^{2}$ . Calculate the length of the wire required to make a 20 $Ω$ coil.

98.

What is meant by the resistance of a conductor? Name and define its SI unit. List the factors on which the resistance of a conductor depends. How is the resistance of a wire affected, if (i) its length is doubled, (ii) its radius is doubled?

99.

(i) A current of 1 A flows in a series circuit having an electric lamp and a conductor of 5 $Ω$ when connected to a 10 V battery. Calculate the resistance of the electric lamp.
(ii) Now, if resistance of 10 $Ω$ is connected in parallel with this series combination, then what change (if any) in current flowing through 5 $Ω$ conductor and potential difference across the lamp will take place? Give reason.

100.

How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery?

101.

(i) Find the value of current I in the circuit given as below:

(ii) You have four resistors of 8 $Ω$ each. Show how would you connect these resistors to have effective resistance of 8 $Ω$ ?

102.

Two resistances when connected in parallel give resultant value of 2 $Ω$ , when connected in series the value becomes 9 $Ω$ . Calculate the value of each resistance.

103.

How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistance in series connected to a battery?

104.

(i) The potential difference between two points in an electrical circuit is 1 V. What does it mean? Name a device that helps to measure the potential difference across a conductor.
(ii) Why does the connecting cord of an electric heater not glow while the heating element does?
(iii) Electrical resistivities of some substances at $20 °$ C are given as below:
$\begin{matrix} S i l v e r & : 1.60 \times 10^{- 8} Ω - m \\ C o p p e r & : 1.62 \times 10^{- 8} Ω - m \\ T u n g s t e n & : 5.2 \times 10^{- 8} Ω - m \\ I r o n & : 10.0 \times 10^{- 8} Ω - m \\ m e r c u r y & : 94.0 \times 10^{- 8} Ω - m \\ N i c h r o m e & : 100 \times 10^{- 6} Ω - m \end{matrix}$
Answer the following questions using the above data:
(a) Among silver and copper, which one is a better conductor and why?
(b) Which material would you advise to be used in electrical heating devices and why?

105.

(i) Heating elements of electrical heating devices is made up of an alloy rather than a pure metal. Given two reasons.
(ii) Four resistors of 4 $Ω$ each are joined end to end to form a square. Calculate the equivalent resistance of the combination between two adjacent corners?

106.

Obtain an expression for the heat produced in a conductor when a voltage V is applied across it. Heating effect of electric current is desirable as well as undesirable. Explain this statement.

107.

$B_{1}, B_{2} a n d B_{3} a r e t h r e e i d e n t i c a l b u l b s c o n n e c t e d a s s h o w n i n f i g u r e . A m m e t e r s A_{1}, A_{2} a n d A_{3} a r e c o n n e c t e d a s s h o w n i n f i g u r e . W h e n a l l t h e b u l b s g l o w, t h e n t h e c u r r e n t o f 3 A i s r e c o r d e d b y a m m e t e r A . (i) W h a t h a p p e n s t o t h e g l o w o f t h e o t h e r t w o b u l b s w h e n b u l b B_{1} g e t s f u s e d ? (i i) W h a t h a p p e n s t o t h e r e a d i n g o f A_{1}, A_{2}, A_{3} a n d A w h e n t h e b u l b B_{2} g e t s f u s e d ? (i i i) H o w m u c h p o w e r i s d i s s i p a t e d i n t h e c i r c u i t w h e n a l l t h e t h r e e b u l b s g l o w t o g e t h e r ?$

108.

(i) Which is the better way to connect lights and other appliances in the domestic circuit, series connection or parallel connection? Justify your answer.
(ii) An electrician has made an electric circuit of a house in such a way that, if a lamp gets fused in a room of the house, then all the lamps in other rooms of the house stop working. What is the defect in this type of circuit wiring ? Give reason.

109.

Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another set of three bulbs of the same wattage are connected in parallel to the source.
(i) will the bulb in the two circuits glow with the same brightness? Justify your answer.
(ii) Now, let one bulb in both the circuits get fused. will the rest of the bulbs continue to glow in each circuit? Give reason.

110.

A household uses the following electric appliances:
(i) The refrigerator of rating 400 W for 10 h each day.
(ii) Two electric fans of rating 80 W each for 6 h daily.
(iii) Six electric tubes of rating 18 W each for 6 h daily.
Calculate the electricity bill for the household for the month of June, if the cost of electrical energy is Rs 3 per unit.

111.

Draw a circuit diagram to show experimental set up for verification of Ohm's law.

112.

How will the reading of V change, if it is connected between B and C? Justify your answer.

113.

The rest positions of the pointers of a milliammeter and voltmeter not in use are as shown in Fig A. When a student uses these in his experiment, then the reading of pointers are in position shown in Fig B. Calculate the corrected value of current and voltage in this experiment.

114.

Electric current I and potential difference V are shown in the following figures across a resistor
(i) What are the reading of volotmeter and ammeter in the given
(ii) Calculate resistance

115.

In the evening, Seema parked her car inside her garage and left for a vacation of 15 days. On returning, she tried to start the car but the car did not start. She checked the fuel and engine oil but that was also full. So she called a mechanic.
After examining the car, the mechanic connected the charge battery with that of a car battery. Then, the car started at once.
On the basis of the above passage, answer the following questions
(i) In which combination, the batteries are connected?
(ii) Draw a circuit diagram for the above-said combination.
(iii) Identify the moral values we get from the passage.

116.

Vishwajeet was doing an experiment by using an ammeter. Suddenly, it fell from his hand and broke. He was fearing that he might be scolded by his teacher. His classmate advised him not to tell the teacher but he refused and told his teacher. on listening to him patiently, the teacher did not scold him as it was just an incident and used the opportunity to show the whole class the internal structure of ammeter.
On the basis of the above passage, answer the following questions:
(i) What are the values displayed by Vishwajeet?
(ii) What is the use of ammeter? How is it connected in the circuit?
(iii) State the aim of anyone experiment, where Vishwajeet could have used the ammeter.

117.

Radhika is a student of class X. Her mother was making tea in an old electric kettle having a metal case. When she switched on the power supply to the electric kettle. She got a severe electric shock. Radhika put off the main switch quickly and found that the connecting cord was torn, where her mother touched the metal case of the kettle. She also found that the red and black wires of connecting cord were firmly connected to the two lower terminals of the power plug but the green wire of cord was not connected to the upper terminal of the plug. Radhika replaced the torn connecting cord and also connected to the three wires of cord firmly to the power plug terminals.
On the basis of the above passage, answer the following questions:
(i) Why did Radhika put off the main switch quickly?
(ii) Which wire red, black or green, touched the metal case of the electric kettle when Radhika's mother got an electric shock?
(iii) What value are displayed by Radhika in this incident?

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