Download 1.1 Short Questions

CURRENT – ELECTRICITY
1.
25. By considering n wires each of equal resistance R, Find the ratio of maximum
resistance to minimum resistance?(HSEB2058)
26. A wire is stretched to double its length, what happens to its resistance &
resistivity? (HSEB 2065)
27. A wire of resistance R is bent to for a complete circle. Find its resistance between
two diametrically opposite points.
28. Explain the significance of shunt with fig. (HSEB2062)
29. Why is an ammeter connected in series where as voltmeter is connected in
parallel circuit combination?(HSEB2056)
30. What happen when ammeter is connected in parallel where as voltmeter is
connected in series combination of circuit?
31. What characteristics should the materials of the fuse and shunts have?
32. There is an impression among many people that a person touching a high power
line gets attack with the line, is it true?
33. You are given two wires each of resistance R, what is the ratio of maximum to
minimum resistance that can be obtained from these wires?(HSEB2064)
Direct Current Circuit
1.1 Short Questions
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A wire is a carrying current, is it charged, why?
Why there is no current until a p.d. is established across the metallic conductor
though it contains large no. Of free electrons moving constantly?(HSEB2061)
An electric bulb lights up almost instantly when switched on although the drift
velocity of electron is very small, why?
Why we do not consider the drift velocity of positive ions?
Calculate the no. Of electrons passing through any cross section of Cu wire in 1.6
sec if 1A current flows through it. Do all the electrons contribute the current?
The electrons drift in a conductor arises due to the force experienced by
electrons in the electric field. This force should cause acceleration of electrons,
but the electrons acquire a steady drift velocity why?
The thermal speeds of the free electrons in a conductor are quite large. Then
why do not they escape from the surface of the conductor?
Current is vector or scalar, justify it.
What causes the resistance to arise?
What are the factors on which the resistance of a conductor
depends?(HSEB2057)
Resistance or resistivity of a conductor is constant. Explain.
Why do the resistances of the conductor increase with increase of temperature?
Distinguish between resistance and resistivity.
What are the factors on which resistivity depend.
What are the characteristics of good resistor?
What types of materials are used as the heating elements?
Why is copper used as connecting wire?(HSEB2056)
Why are standard resistors made of alloys such as constantan and
manganin?(HSEB2060)
Two wires one of cu and another of manganin have equal lengths and equal
resistance, which wire is thicker?
The drift velocity of electron in conductor is very small but how large current is
produced?
What is the change in resistance & resistivity of a conductor when it is cut (i)
longitudinally & (ii) transversely?
Ohm’s law is not universal, justify it.
Distinguish between ohmic & non-ohmic conductors.
Why the conductivity of metals decrease with the increase in temperature?
1.2 Long Questions
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State and explain ohms law. How would you verify it experimentally?
What is drift velocity? Derive an expression for the drift velocity of an
electron in a conductor. (HSEB 2060)
What is a shunt? Derive an expression for the current flowing through
galvanometer and shunt. Mention the uses of shunt.
What is resistance of conductor? Derive an expression for the equivalent
resistance when three resistors are conducted in series.
What is a galvanometer? How would you convert it in to an ammeter?
(HSEB 2063,2057)
What is a voltmeter? How a galvanometer is converted in to a voltmeter?
1.3
Numericals
1.
In Hydrogen atom, the electron makes 6.6x1015 revolutions/ sec. around
the nucleus in the orbit of radius 0.5Ǻ.What is the equivalent current?
(1.06x10-3 A)
2.
An α-particle (mass =4mp ‘charge 2e) is revolving in a circular orbit of radius
1Ǻ,with speed 3.14x106m/s. What is the equivalent current? (1.6x10-3 A)
3.
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A thin film resistor in a solid-state circuit has a thickness of 1m and is made of
nichrome of resistivity 10-6 Wm. Calculate the resistance available between
opposite edges of a 1mm2 area of film (a) if it is squared shaped, (b) if it is
rectangular, 20 times as it is wide. (a) 1W (b) 20W (c) 0.05W
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reading to 1 A? (0.05W)
13 A galvanometer can bear maximum current of 25mA and resistance 5W. Find
suitable resistance to convert it in to 9
a. a voltmeter of range 0 - 2 V
b. an ammeter of range 0 – 10 Amp.(HSEB2065) (i) 80W (ii) 0.0125W
The resistance of an iron wire and a copper wire at 20o are 3.9W and 4.1W
respectively. At what temperature will the resistance be equal? Temperature
coefficient of resistivity for iron is 5x10-3 k-1and for copper is 4x10-3 k1 Neglect any
thermal expansion. (84.50 C)
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A copper wire of cross section 3x10 –6 m2 is carrying a current of 4.2A. Calculate
current density in the wire and the drift velocity of electrons if the number of
conduction electrons per unit volume is n =8.4x10 28 m-3. (1.04x10-4 m s -1)
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If 10 m long manganin wire, 0.13 cm in diameter has resistance of 3.4W, find the
conductivity and resistivity of manganin. (2.2x106 sm-1)
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Calculate the equivalent between A and me in the circuit. (RAB =R/3W)
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A wire has a resistance of 32W. It is extended to double its original length.
Calculate the resistance and resistivity of the wire and percentage change in
resistance. (300%)
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An infinite ladder network is constructed with 1W and 2W resistance as shown in
fig. Find the effective resistance between A and B.(R= 2W)
14 Copper has 8.5x 10 28 free electrons per cubic meter. A 71.0 cm length of 12
gauge copper wire, that is 2.05 mm in diameter, carries 4.85 A of current (a) How
much time does it take for an electron to travel the length of the wire? (b)
Repeat part (a) for 6-gauge copper wire (diameter 4.12 mm) of the same length
that carries the same current. (a) 110m (b) 441.6m
15 A copper wire has a square cross section 2.3 mm on a side. The wire is 4.0 m long
and carries a current of 3.6 A. The density of free electrons is 8.5x 10 28/ m3. Find
the magnitudes of (a) the current density in the wire; (b) the electric field in the
wire, (c) How much time is required for an electron to travel the length of the
wire? (a) 867x106 A/m2 (b) 0.149V/m (c) 104.6 min
16 In an experiment conducted at room temperature, a current of 0.820 A flows
through a wire 3.26 mm in diameter. Find the magnitude of the electric field in
the wire if the wire is made of (a) tungsten, (b) aluminum. (a) 5.16x10-3 V/m (b)
2.70x10-3 V/m)
17 A wire of length L and cross sectional area A has resistance R. What will the
resistance of the wire e if it is stretched to twice its original length? Assume the
density and resistivity of the material do not change when the wire is stretched.
(4 R)
10 In the given circuit find the value of I, I2, I2, I3, and I4. (I=3.5A, I1=1A, I2=2.5A,
I3=I4=1.25A)
11 Find the potential difference between the points B and D in the network given
below. (IV)
18 The potential difference between points in a wire 75.0 cm apart is 0.938 V when
the current density is 4.40 x 10 7 A/m2. What is (a) the magnitude of E in the
wire? (b) The resistivity of the material of which the wire is made? (a) 1.25V/m
(b) 2.84x10-8 Wm)
19 (a) What is the resistance of a Nichrome wire at 0.0o C if its resistance is 100.00W
at11.5o C? (b) What is the resistance of a carbon rod at 25.8o C if its resistance
is 0.016W at 0.0o C? (a) 99.54W (b) 0.0158V)
20 A moving coil meter has a resistance of 25W, 2.40W and indicates full-scale
deflection when a current of a 4.0mA flows through it. How could this meter be
converted to a millimeter having a full-scale deflection for a current of 50mA?
12 A galvanometer with a scale divided in to 100 equal divisions has a current
sensitivity of 10-division per milliampere and a voltage sensitivity of 2 divisions
per millivolt. How can the instrument be adapted to serve as an ammeter
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(2.17W)
2.2 Long Questions
21 A moving coil has a resistance of 25W and indicates full-scale deflection when a
current of 4mA flows through it. How could this meter be converted (i) to a
voltmeter with 0 – 3 V range. (ii) To an ammeter 0 – 1 A range. (725W, 0.10W)
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Emf. Of cell & Heating effect of current
2.1 Short Questions
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State and explain Joule’s law of heating. Deduce an expression for the heat
developed in a wire by the passage of an electric current. (HSEB 2056)
Describe an experiment to verify to Joules law of heating.
Define emp, terminal p.d. and terminal resistance of a cell. Derive a relation
between them.
What is series combination of cells? What is the condition for maximum current
in this combination?
What is the parallel combination of cell? What is the condition for maximum
current in this combination?
What is the mixed grouping of cells? What is the condition for maximum current
in this grouping?
2.3 Numericals
Why is heat produced when current is passed across the conductor?
Why is it easier to start a car engine on a hot day than on a cold day?
Heater wire gets red hot while the cable carrying current remains cold, justify it.
What is internal resistance of cell? On what factors it depend?
Distinguish between e.m.f & terminal.p.d.
Electric current is flowing in a metallic conductor when the conductor is heated
up; cold water is poured over half the conductor. What could be the effect on
the temperature of the other half of the conductor?
Emf is not always grater than terminal p.d, justified.(HSEB2058)
Is it possible that there is no p.d. between the terminals of the cell?
High voltage power supply must have a very high internal resistance, why?
Two bulbs of 60 watt & 1000 watt are connected in parallel & series combination
for same power supply, which would shine more?(HSEB2057)
Why large heat in produced when battery is short-circuited?
Two bulbs have the filament of the same length. If one is of 40 watt & another is
60 watt which one has thicker filament?
Light of bathroom bulb gets dimmer for a moment when geyser is switched on,
why?
When a motor car is started, its light becomes slightly dim, why? (HSEB2065)
The element of heater is very hot while the wire carrying current are cold, why?
(SHEB 2064)
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A battery of emf 4V and internal resistance 2W. Calculate the terminal p.d. What
additional resistance in series with the 8W resistor would produce a terminal
p.d.of 3.6V? (3.2V,10W)
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A battery of emf 24V and internal resistance r is connected to a circuit having
two parallel resistors of 3W and 6W in series with an 8W resistor. The current
flowing in the 3W resistor is then 0.8A. Calculate (i) the current in the 6W
resistors, (ii) r, (iii) the terminal p.d. of the battery. (i) 1.2A (ii) 10W (iii) 12V
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A battery x of emf 6V and internal resistance 2W is in series with a battery Y of
emf 4V and internal resistance 8W so that the two emfs act in the same
direction. A 10W resistor is connected batteries. Calculate the terminal p.d. of
each battery. (Vx = 5V VY = 0V, Vx1 =5.8V, Vy 1 = 4.8W )
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Two resistors of 1200W and 800W are connected in series with a battery of emf
24V and negligible internal resistance. What is the p.d. across each resistor? A
voltmeter V of resistance 600W is now connected firstly across the 1200W
resistor and then across 800 resistor. Find the p.d recorded by the voltmeter in
each case? ( 14.4V,9.6V, 8V, 5.3V)
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A voltmeter having a resistance of 1800W is used to measure the potential
difference across a 200W resistance which is connected to the terminals of a d.c.
power supply having an emf of 50V and an internal resistance of 20W. Determine
the percentage change in the potential difference across the 200W resistor as a
result of connecting the voltmeter across it. (-1%)
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11 A typical small flashlight contains two batteries, each having an emf of 1.5 V,
connected in series with a bulb having resistance 17W. (a) If the internal
resistance of the batteries is negligible, what power is delivered to the bulb? (b)
If the batteries last for 5.0 h, what is the total energy delivered to the bulb? (
0.528W, 9.5x103 J)
What is the potential difference between the point B and D? What resistor could
you add to the 12W resistor in branch ADC in order to make the potential
difference between B and D zero? ( 2V, 4W)
12 The temperature of 0.3 Kg of paraffin coil in a vacuum flask rises 1.0o C per
minute with an immersion heater of 12.3 watts input. On repeating with 0.4 kg of
oil the temperature reses by 1.20 C per minute for an input of 19.2 watts. find the
specific heat capacity of the oil and the thermal capacity ( assumed constant) of
the flask.(72J K-1 )
13 Find the current delivered by the battery in the circuit shown below.( 2.93A)
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A heating coil of power rating 10W is required when the p.d. across it is 20V.
calculate the length of nichrome wire needed to make the coil if the
cross-sectional area of wire used is 1x10-7 m2 and the resistivity of nichrome is
1x10-6 Wm. What length of wire would be needed if its diameter was half that
previously used? ( 4m, 1m)
14 Find the equivalent resistance between the terminals points x and Y in the
circuit. Take the resistance of each resistor 10W. (12W)
15 Twelve cells each of emf 2V and internal resistance½ W are arranged in a battery
of n rows and an external resistance of 3/8W is connected to the poles of the
battery. Determine the current flowing through the resistance in terms of n. Find
the internal resistance of the battery when maximum current is produced. (
64n/n2=16 3/8W).(HSEB2062)
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Two lamps rated as 25W-220V and 100W-220V are joined in series and
connected to 220V mains. What power are consumed by the lamps?(16W, 4W)
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An electrical heating coil is connected in series with a resistance of xW across the
240V mains, the coil being immersed in a kilogram of water at 20oC. The
temperature of the water rise to boiling point in 10 minutes. When a second
heating experiment is made with the resistance x short-circuited, the time
required to develop the same quantity of heat is reduced to 6 minutes. Calculate
the value of x . (17.9W, 72 JK-1 )
16 A accumulator of emf 2V and of negligible internal resistance is joined in series
with a resistance of 500W and an unknown resistance xW. The readings of a
voltmeter successively across the 500W resistance and x are2/7W and 8/7W
respectively. Calculate the value of x and the resistance of the voltmeter.
(2000W, 1000W)
10 A battery powered global positioning system (GPS) receiver operating on 9.0 V
draws a current of 0.13 A. How much electrical energy does it consume during
11h? (14.74 x103 J)
17 A battery of emf 1.5v has a p.d. Of 1.25v when resistor of 25W is joined to it.
Calculate the current flowing, the internal resistance and terminal p.d when a
resistor of 10W replaces 25W resistor?(HSEB2060)
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Electrical Circuit
3.1 Short
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The driver cell of a potentiometer has an emf of 2 V and negligible internal
resistance. The potentiometer wire has a resistance of a 3W. Calculate the
resistance needed in series with the wire if p.d. of 5m V is required across the
whole wire. The wire is 100cm long and a balance length of 60 cm obtained for a
thermocouple of emf. E What is the value of E. .(1197W, 3mV) (HSEB 2063,2056)
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The emf of a battery A is balanced by a length of 75 cm on a potentiometer wire.
The emf of a standard cell, 1.02V, is balanced by a length of 50cm. What is the
emf of A? Calculate the new balance length if A has an internal resistance of 2W
and a resistor of 8VW is joined to its terminals.(1.53V, 60cm)
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A 1.0W resistor is in series with an ammeter M in a circuit. The p.d. across the
resistor is balanced by a length of 60 cm on a potentiometer wire. A standard cell
of emf. 1.02V is balanced by a length of 50cm. If M reads 1.10A, what is the error
in reading? (0.124A)
4
In a meter bridge, the gaps are closed by two resistances R1 and R2 and the
balance point is obtained at 40cm. when R2 is shunted by a resistance of 10 Ω,
the balance point shifts to 50cm. What are the values of R 1 and R2? (5W, 3.33W).
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In a meter bridge, the gaps are closed by two resistances R1 and R2 and the
balance point is obtained at 40cm. when R2 is shunted by a resistance of 10 Ω,
the balance point shifts to 50cm. What are the values of R 1 and R2?(3.33Ω,5Ω)
Questions
Why are kirchhoff’s laws preferred over ohm’s law?
Why is wheat stone bridge method preferred over ammeter - voltmeter method
to measure the resistance?
When the resistance is made half than the current is not half of its original valve,
justify it.
On what principle the kirchhoff’s laws based?
Why galvanometer shows null defection at balance condition of wheat stone
bridge method?
What is the principle of potentiometer?
Why is potentiometer used to measure the emf than voltmeter?
How can we increase the sensitivity of wheat stone bridge?
Wheat stone is not suitable to measure the very small and large resistance why?
What is meant by end correction for the meter bridge?
What happen when potentiometer wire is not made uniform?
A potentiometer is equivalent to voltmeter of infinite resistance, explain.
Two bulbs one is filled with gas and other is filled with vacuum are connected in
series combination which one gives brighter light?
3.2 Long Questions
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State and explain Kirchhoff’s law with suitable circuit diagram.
Describe the Wheatstone bridge circuit and deduce the condition for balance
using Kirchhoff’s law.
What is the principle of Wheatstone bridge? How it applied to find unknown
resistance?
What is principle of a potentiometer? How can you use it to find resistance of a
cell?(HSEB 2065, 2062,2060)
What is potentiometer? Explain how you would use it to compare the emfs of
two cells. (HSEB 2057)
What is a meter bridge? How would you use it to measure unknown resistance?
What is a P.O. Box? How would you use a P.O .Box to measure unknown
resistance?
4.
Thermoelectric effect
4.1 Short Questions
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3.3 Numericals
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What is the cause of electric current in thermoelectricity?
How seebeck effect is different from Peltier effect? Explain.(2062)
What is thermoelectric series?
What are factors on which thermo emf. Depends?(HSEB2061)
Why do we generally prefer Sb-Bi than Fe-Cu thermocouple?(HSEB2060)
Peltier effect is inverse of Seebeck effect, explain.
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atoms of copper, Cu2+ and of silver which are liberated respectively by the Faraday .
(b) the masses of the two elements liberated respectively by 0.5 A in 10 min. (
Electronic charge, e = - 1.6 x10-19 C).(6×10 23)
Distinguish between joules and seebeck heating effect.
What do you mean by inversion temperature? On what factor does it depend?
(HSEB2065)
What do you mean by Peltier’s effect?(HSEB2058)
4.2 Long Questions
What do you mean by thermo electric effect? Discuss the variation of thermo
emf in a thermo couple with the change in temperature. (HSEB 2063,2057)
What is thermo electric current? Describe Seebeck and Peltier effect?
Define neutral temperature and temperature of inversion. Give the relation
between them.
What is Thomson’s effect? What is its cause?
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Distinguish between ionic and electric current.
Why is voltameter preferred than ammeter to measure the current?(HSEB2064)
Why do the electrolytes have lower conductivity than metallic conductor?
Can ac be used in electrolysis process?
Define the terms ece., ce., Faraday’s constant.(HSEB2056)
5.2
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Calculate the charge needed to deposit 2g of oxygen in the electrolysis of water.(
Relative molecular mass of oxygen is 32, F = 96500 c-1 ) (HSEB2057)
4.
If an electric current passes through a copper voltameter and a water voltmeter in
series, calculate the volume of hydrogen which will be liberated in the latter, at 250 C
and780 mm Hg pressure, whilst 5x10-5 Kg of copper is deposited in the former.
(Take mass of hydrogen deposited per coulomb as 1.04x10-8 Kg C-1 , of copper as
3.3x10-7Kg C-1 , density of hydrogen as 9x10-2 Kg m -3 at s.t.p.) (18.6 cm3)
5.
A copper refining cell consists of two parallel plate electrodes, 6cm apart and 1 m
square, immersed in copper sulphate solution of resistivity 1.2x10 -2 Wm, calculate
the p.d. which must be established between the plates to provide a constant current
to deposit 0.48 Kg of copper on the cathode in one hour. (Mass of copper liberated
per coulomb z = 3.89x10-7 Kg C-1 ).
(0.29V)
Chemical effect of current
5.1 Short Questions
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Long Questions
What is electrolysis? State and explain Faraday’s laws of electrolysis. How they
are experimentally verified?(HSEB 2065,20662)
State
Faraday’s laws of electrolysis. Derive the relations connecting chemical
equivalent and electrochemical of an element.
5.3
Numericals
1.
Assuming the Faraday constant F is 96500 C mol-1 , calculate (i) the charge needed to
deposit 1.6 gm of the oxygen in the electrolysis of water, (ii) the time required if a
steady current of 2.5 A is used, (iii) the mass of hydrogen deposited at the end of the
time. (Relative molecular mass of hydrogen and oxygen = 2 and 32
respectively).(19300C, 7720Sec, 0.2×10 -3 Kg)
2.
Assuming the Faraday constant F is 96500 C mol-1 and that the relative atomic
masses of copper and silver are 63 and 108 respectively, calculate (i) the number of
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