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A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the ratio R/R' is :
(a) 1/25 (b) 1/5 (c) 5 (d) 25
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Which of the following terms
does not represent electrical power in a circuit?
(a)
I2R (b)
IR2 (c)
VI (d) V2/R
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An electric bulb is rated 220
V and 100 W. When it is operated on 110 V, the power consumed will be:
(a)
100 W (b) 75 W (c) 50 W (d)
25 W
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Two conducting wires of the
same material and of equal lengths and equal diameters are first connected in
series and then in parallel in an electric circuit. The ratio of the heat
produced in series and parallel combinations would be
(a)
1 : 2 (b) 2 : 1 (c) 1 : 4 (d)
4 : 1
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How is voltmeter connected in the circuit to measure potential difference
between two points?
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A copper wire has a diameter of 0.5 mm and a resistivity of 1.6 ×
10?6 
. How much of
this wire would be required to make a 10 
coil? How much
does the resistance change if the diameter is doubled?
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The values of current, I,
flowing in a given resistor for the corresponding values of potential
difference, V, across the resistor are given below :
I (ampere) : 0.5 1.0 2.0 3.0 4.0
V (volt) : 1.6 3.4 6.7 10.2 13.2
Plot
a graph between V and I and calculate the resistance of the resistor.
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When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
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A battery of 9 V is connected in series with resistors of 0.2
, 0.3, 0.4, 0.5 and 12. How much
current would flow through the 12 resistor?
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How many 176
resistors (in
parallel) are required to carry 5 A in 220 V line?
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Show how you would connect three resistors, each of resistance 6
, so that the
combination has a resistance of (i) 9 (ii) 2.
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Several electric bulbs designed to be used on a 220 V electric
supply line, are rated 10 W. How many lamps can be connected in parallel with
each other across the two wires of 220 V line if the maximum allowable current
is 5 A?
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A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24
resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
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Compare the power used in the
2
resistor in each
of the following circuits :
(i)
a 6 V battery in series with 1 and 2 resistors, and
(ii) a 4 V battery in parallel with 12 and 2 resistors.
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Two lamps, one rated 100 W at 220 V, and the other 60 W at 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?
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Which uses more energy, a 250 W TV set in 1 h, or a 1200 W toaster
in 10 minutes?
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An electric heater of resistance 8
draws 15 A from
the service mains for 2 hour. Calculate the rate at which heat is developed in
the heater.
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Explain the following :
(a) Why is tungsten used almost exclusively for filament of incandescent lamps?
(b) Why are the conductors of electric heating devices, such as toasters and electric irons, made of an alloy rather than a pure metal?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its cross-sectional area?
(e) Why are copper and aluminium wires usually employed for electricity transmission.
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What does an electric circuit mean?
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Define the unit of current.
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Calculate the number of electrons constituting one coulomb of charge.
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Name a device that helps to maintain a potential difference across a conductor.
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What is meant by saying that the potential difference between two points is 1 V?
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How much energy is given to each coulomb of charge passing through a 6 V battery?
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On what factors does the resistance of a conductor depend?
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Will current flow more easily through a thick wire or a thin wire of the same material when connected to the same source? Why?
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Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half its former value. What change will occur in the current through it?
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Why are the coils of electric toasters and electric irons made of an alloy rather than a pure metal?
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Use the data in Table 12.2 in NCERT to answer the following :
(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?
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Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a
, resistor, a
resistor, and a resistor, and a plug key, all connected in series.
-
Redraw the circuit of question-12, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the
resistor. What would be the reading in the ammeter and the voltmeter?
-
Judge the equivalent resistance when the following are connected in parallel:
(a)
and
, (b)
and
and
-
An electric lamp of
a toaster of resistance
, and a water filter of resistance
, 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 three appliances and what is the current through it?
-
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series.
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How can three resistors of resistances 2
, 3
and 6
be
connected to give a total resistance of
(a)
(b)
?
-
What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistances
-
Why does the cord of an electric heater not glow while the heating element does?
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Compute the heat generated while transferring 96000 coulombs of charge in one hour through a potential difference of 50 V.
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An electric iron of resistance
,
takes a current of 5 A. Calculate the heat generated in 30 s.
-
What determines the rate at which energy is delivered by a current?
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An electric motor takes 5 A from a 220 V line. Determine the power and energy consumed in 2h.
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question_answer42)
A cell, a resistor, a key and an ammeter are arranged as shown in the
circuit diagrams of figure. The current recorded in the ammeter will be
(a) maximum in (i) (b)
maximum in (ii)
(c) maximum in (iii) (d)
the same in all the cases
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question_answer43)
In the following circuits, heat produced in the resistor or combination
of resistors connected to a 12 V battery will. be
(a) same in all the cases (b)
maximum in case (i)
(c) maximum in case (ii) (d)
maximum in case (iii)
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question_answer44)
Electrical resistivity of a given metallic wire depends upon
(a) its length (b) its thickness (c)
its shape (d) nature of the material
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question_answer45)
A current of 1 A is drawn by a filament of an electric bulb. Number of electron
passing through a cross-section of the filament in 168 would be roughly
(a)
(b)
(c)
(d)
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question_answer46)
Identify the circuit in which the electrical components
have been properly connected.
(a)
(i) (b) (ii) (c)
(iii) (d) (iv)
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question_answer47)
What is the maximum resistance which can be made using
five resistors each of
?
(a) (b)
(c)
(d)
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question_answer48)
What is the minimum resistance which can be made using five resistors each
of ?
(a) (b)
(c)
(d)
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question_answer49)
The proper representation of series combination of cells obtaining maximum
potential is
(a)(i) (b) (ii) (c)
(iii) (d) (iv)
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question_answer50)
Which of the following represents voltage?
(a)
(b)
Work done x Charge
(c)
(d)
done x Charge x Time
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question_answer51)
A cylindrical conductor of length 
and uniform area of
crossection A has resistance R. Another conductor of length 21 and resistance R
of the same material has area of cross-section.
(a) A/2 (b) 3A/2 (c)
2A (d) 3A
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question_answer52)
A student carries out an experiment and plots the V -I graph of three samples
of nichrome wire with resistances 
and
respectively as shown
in figure. Which of the following is true?
(a)
(b)
(c)
(d)
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question_answer53)
If the current I through a resistor is increased by 100%
(assume that temperature remains unchanged), the increase in power dissipated
will be
(a) 100% (b) 200% (c)300%
(d) 400%
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question_answer54)
The resistivity does not change if
(a) the material is changed (b)
the temperature is changed
(c) the shape of the resistor is changed (d)
both material and temperature are changed
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question_answer55)
In an electrical circuit three incandescent bulbs. A, B and C of
rating40W, 60 W and 100 W, respectively are connected in parallel to an electric
source. Which of the following is likely to happen regarding their brightness?
(a) Brightness of all the bulbs will be the same
(b) Brightness of bulb A will be the maximum
(c) Brightness of bulb B will be more than that of A
(d) Brightness of bulb C will be less than that of 6
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question_answer56)
In an electrical circuit, two resistors of 
and 
respectively are connected
in series to a 6V battery. The heat dissipated by the resistor in 5s will
be
(a)5 J (b)10 J (c)20
J (d) 30 J
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question_answer57)
An electric kettle consumes 1 kW of electric power when
operated at 220V. A fuse wire of what rating must be used for it?
(a) 1 A (b) 2
A (c) 4 A (d)
5 A
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question_answer58)
Two resistors of resistance and when connected to a
battery will have
(a) same current flowing through them when connected in
parallel
(b) same current flowing through them when connected in
series
(c) same potential difference across them when connected
in series
(d) different potential difference across them when
connected in parallel
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question_answer59)
Unit of electric power may also be expressed as
(a) volt ampere (b) kilowatt hour (c)
watt second (d) joule second
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question_answer60)
A child has drawn the electric circuit to study Ohm's law as shown in figure.
His teacher told that the circuit diagram needs correction. Study the circuit
diagram and redraw it after making all corrections.
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question_answer61)
Three 
resistors,
A, B and C are connected as shown in figure. Each of them dissipates energy and
can with stand a maximum .power of 18 W without melting. Find the maximum
current that can flow through the three resistors?
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question_answer62)
Should the resistance of an ammeter be low or high? Give reason.
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question_answer63)
Draw a circuit diagram of an electric circuit containing a cell, a key, ammeter,
a resistor of in series
with a combination of two resistors(
each)
in parallel and a voltmeter across the parallel combination.
Will the potential difference across the resistors be the
same as that across the parallel combination of resistors? Give
reason.
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question_answer64)
How does use of a fuse wire protect electrical appliances?
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question_answer65)
What is electrical resistivity? In a series electrical circuit comprising
a resistor made up of a metallic wire, the ammeter reads 5A. The reading of the
ammeter decreases to half when the length of the wire is doubled.' Why ?
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question_answer66)
What is the commercial unit of electrical energy? Represent it in terms of
joules.
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question_answer67)
A current of 1 A flows in a series circuit containing an
electric lamp and a conductor of 
when
connected to a 10V battery. Calculate the resistance of the electric lamp.
Now, if a resistance of 
is connected in
parallel with this series combination, what change (if any) in current flowing
through conductor and
potential difference across the lamp will take place? Give reason.
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question_answer68)
Why is parallel arrangement used in domestic wiring?
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question_answer69)
and 
three identical
bulbs connected as shown in figure. When all the three bulbs glow, a current of
3A is recorded by the ammeter A.
(i) What happens to the glow of the other two bulbs when
the bulb 
gets fused?
(ii) What happens to the reading of 
and A when the bulb 
gets fused?
(iii) How much power is dissipated in the circuit when all
the three bulbs glow together?
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question_answer70)
There 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 same source.
(a) Will the bulb in the two circuits glow with the same
brightness ?Justify your answer
(b) Now let one bulb in both the circuits get fused. Will
the rest of the bulbs continue to glow in each circuit? Give reason
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question_answer71)
State Ohm's law? How can it be verified experimentally?
Does it hold good under all conditions? Comment.
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question_answer72)
What is electrical resistivity of a material? What is its
unit? Describe an experiment to study the factors on which the resistance of
conducting wire depends.
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question_answer73)
How will you infer with the help of an experiment that the
same current flows through every part of the circuit containing three
resistances in series connected to a battery?
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question_answer74)
How will you conclude that the same potential difference
(voltage)exists across three resistors connected in a parallel arrangement to a
battery?
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question_answer75)
What is Joule's heating effect? How can it be demonstrated
experimentally ? List its four applications in daily life.
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question_answer76)
Find out the following -in the electric circuit given in
figure
(a) effective resistance of two 
resistors in the
combination
(b) current flowing through resistor
(c) potential difference across resistance
(d)power dissipated in resistor
(e) difference in ammeter readings, if any
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