Thursday, June 11, 2015
Tuesday, June 2, 2015
IMPORTANT QUESTIONS FOR CLASS – XII
Electrostatics
Q.1 why can one
ignore quantization of charge when dealing with macroscopic charges?
Q.2 what orientation
of an electric dipole in a uniform electric field corresponds to stable
equilibrium?
Q.3 Name the
physical quantity whose SI unit is JC-1.Is it a scalar or a vector
quantity?
Q.4 what is the
amount of work done in moving 100 µC charge between two points 5 cm apart
on an equipotential
surface?
Q.5 The distance of
the field point on the axis of a small electric dipole is doubled. By what
factor
will the electric
field due to the dipole change?
Q.6 In a parallel
plate capacitor the potential difference of 102 V is maintained
between the plates.
What will be electric field at points A
and B.?
 |
. A
. B
|
Q.7.A Gaussian surface encloses an electric dipole within it. What is the total flux across sphere?
Q.8 What is the angle between the directions of electric field at any
(i) axial point
Q9.
The given graph shows that the variation of charge versus potential difference
V for the two
capacitors
C1 & C2. The two capacitors have same plate separation but the plate area
of C2 is
doubled
than that of C1.Which of the line in the
graph corresponds to C1 &C2 and why?
Q10.
A point charge q is placed at O as shown in the figure.
Is VP-VQ +ve or
–ve when (i) q>0, (ii) q<0? Justify your answer.
Q11.
Why does the electric field inside a dielectric decrease when it is placed in
an external electric field?
Q12.
A charged particle is free to move in an electric field. Will it always move
along an electric line of force?
Q13.
If V (=q/4πεor) is the potential at a distance r due to a point charge q, then
determine the electric field
due
to a point charge q, at a distance r.
Q14.
Draw an arrangement of three point charges separated by finite distances, that has
zero electric
Potential
energy.
Q15.
Charge of 2C is placed at the centre of a cube of volume 8 cm3. What
is the electric flux passing
through
one face?
OR
Three charges, each equal to +2C are placed at
the corners of an equilateral triangle.
If the force between any two charges be
F, then what will be the net force on either Charge?
Q16.
A charged particle q is shot towards another charged particle Q which is fixed,
with a speed v. It
approaches
Q up to a closest distance r and then returns. If q were given a speed 2v,then
find the
closest
distance of approach.
Q17.
Two capacitors of capacitance 6mF and 12mF are connected in series with the
battery .The voltage
across
the 6mF capacitor is 2 volt .Compute the total battery voltage.
Q18.
Five identical capacitors, each of capacitance C are connected between points X
and
Y
as shown in the figure. If the equivalent capacitance of the combination
between X and Y is 5mF.
Calculate the capacitance of each
capacitor.
Q19.
A parallel plate capacitor with air between the plates has a capacitance of 8
pF . The separation
between
the plates is now reduced by half and the space between them is filled with a
medium of
dielectric
constant 5. Calculate the value of capacitance of parallel plate capacitor in
second case.
Q20.
A uniform electric field of 2 kNC-1 is in the x-direction. A point
charge of 3 μC initially at rest at the
origin
is released. What is the kinetic energy of this charge at x = 4m?
Q.21.
Two identical metal plates are given the charges Q1 and Q2
(Q2< Q1) respectively. If they are now
brought
close together to form a parallel plate capacitor with capacitance C then what
is the potential
difference
between them?
Q22.
Three charges Q, +q and +q are placed at the vertices of a right angle
isosceles triangle as shown.
Find the magnitude of Q for which net
electrostatic energy of the configuration is zero.
Q.23.
A charge Q is distributed over the two concentric hollow spheres of radii ‘r’
and ‘R’(R>r) such that
the
surface densities are equal. Find the potential at the common centre.
Q.24.
An electric dipole is held in an uniform electric field. Using suitable
diagram, show that it doesn’t
undergo
any translatory motion, and (ii)Derive an expression for torque acting on it
and specify its direction.
Q25.
The field potential inside a charged ball depends only on the distance from its
centre as
V=ar2+b, where a and b are
constants. Find the space charge distribution r(r) inside the ball.
Q26.
Four charges each having charge ‘q’ are
along x-axis at x=1 cm ,x=2 cm, x=4 cm,x=8 cm .
Find the electric field at x=0 due to these
charges.
OR
A
4µF capacitor is charged by a 200V supply. The supply is then disconnected and
the charged capacitor is connected to another uncharged 2µF capacitor. How much
electrostatic energy of the first capacitor is lost in the process of attaining
the steady situation?
Q27.The electric field in a region is radially outward and
varies with distance r as E=250 r Vm-1.Calculate the charge
contained in a sphere of radius 0.2 m centered at the origin.
Q28.How charge given to inner sphere transfers to outer sphere? Name
the device where it is used. Explain with diagram working of that device
OR
State gauss’s theorem. Use it to find electric field due infinite line
of charge. What is the effect on electric field, when charge density gets
double and distance between point and line of charge is half.
Q.29 There is an isolated parallel plate capacitor of capacitance C
charged to a potential difference V.If the separation between the plates is
doubled, how the following quantities will vary:
(i) Capacitance
(ii)Potential difference
(iii) Charge on the capacitor
(iv) Electric field inside the plates
(v) Energy stored.
OR
What is an electric field? Find an expression for electric field along
the axial line of electric field. Give its SI unit.
Q.30 What is an electric polarization of a dielectric? What is the
effect on capacitance of a capacitor when a dielectric of width‘t’is placed
between the two plates of parallel plate capacitor?
OR
What is electric potential? Give its SI unit. Find the expression for
the electric potential at any point due to a point charge.
RAY OPTICS
1
|
Does critical
angle depend on wavelength used?
|
2
|
Name the
phenomenon responsible for mirage formation.
|
3
|
Does a prism
displace or deviate an incident ray?
|
4
|
What are the
factors on which light reflected from a surface depends?
|
5
|
A thin prism of 600
gives deviation of 300. What is the refractive index of the
material of the prism?
|
6
|
For what angle of
incidence the lateral shift produced by a parallel sided glass slab is
maximum?
|
7
|
What will be the
colour of the sky in the absence of atmosphere?
|
8
|
You are provided
with four lenses of focal lengths 1cm, 3cm, 10cm and 100 cm . Which two would
you prefer for a microscope and which two for a telescope?
|
9
|
How deep will a 4m
tank appear when seen in air due to optical illusion. Refractive index of
water is 4/3.
|
10
|
Name the colour
having the ( i ) minimum speed ( ii ) maximum speed through a prism.
|
11
|
What do you mean
by spherical aberration of a mirror ? How can it be minimized?
|
12
|
Yellow light of
wavelength 589nm is incident on a boundary separating air and glass . Find
the speed , wavelength and frequency for ( i ) reflected light ( ii ) refracted light . Refractive index
of glass for yellow light is 1.5
|
13
|
Two thin lenses
having focal lengths having focal lengths +20cm and -30cm are put in contact
. The doublet behaves as an achromatic lens. Find the focal length of this
doublet. What will be the converging power if the focal length of the two
lenses I s made the same?
|
14
|
Derive mirror
formula for concave mirror forming virtual image.
|
15
|
(i )The refractive
index of glass is 1.5. What is the
time taken by light to travel 1m thickness of the glass ?the speed of light
in vacuum is 3x 108 m/s .
|
16
|
Where should an object be placed from a
converging lens of focal length 20cm so as to obtain a real image of
magnification 2?
|
17
|
Show that angle of
deviation depends on angle of incidence.
|
18
|
Write the
difference between dispersive and non dispersive medium with examples.
|
19
|
Show that lateral
displacement is directly proportional to t and i1.
|
20
|
What is the main
requirement in the fabrication of optical fibres? How it can be achieved? Write two examples
|
21
|
Obtain a relation
for refraction from a rarer to denser medium at a convex spherical surface
forming real image.
|
22
|
Derive thin lens
formula for a concave lens .
|
23
|
What is myopia?
What are its causes? How can it be corrected?
|
24
|
Describe an
astronomical telescope .Derive an expression for its magnifying power when
final image is at
( a ) infinity
( b ) at D
|
25
|
Compound
microscope has an objective lens of focal length 2cm and eye lens of focal
length 5cm. If an object is placed 3cm from the objective and final image is
formed at the least distance of distinct vision, find the magnification
produced.
|
26
|
A double convex
lens made of glass of refractive index 1.5 has both curvatures of radii 20cm.
An object 2cm high is placed 2cm from this lens , find the position, nature
and size of the image.
|
27
|
The angle of
minimum deviation for yellow light in a prism of refractive index 1.6 is
found to be 460. Calculate refracting angle of the prism.
|
28
|
Derive lens makers
formula.
|
29
|
Give the
construction and working of a compound microscope. Define and derive an
equation for its magnifying power.
|
30
|
For refraction
through prism derive prism formula.
|
WAVE OPTICS
1.
What is
the polarizing angle of a medium of refractive index 1.732?
2.
Sketch
the variation of intensity of interference pattern in Young’s double slit
experiment.
3.
What is
the ratio of fringe width of bright and dark fringes in Young’s double slit
experiment?
4.
What is
the effect on interference fringes in Young’s double slit experiment if one
slit is covered?
5.
A
polarizer and analyzer are so oriented that intensity of transmitted light is
maximum. If the analyzer is rotated through 600 what fraction of
maximum light is transmitted?
6.
Draw a
graph showing variation of intensity of polarized light transmitted by an
analyzer.
7.
Bubbles
of a colourless soap solution appear colored in sun light. Why?
8.
What
happens to the energy at destructive interference in interference pattern?
9.
What
will be the effect on interference fringes in Young’s double slit experiment if
(i) Monochromatic source is replaced by white light; (ii) Screen is moved away
from the slit. Justify your answer.
10.
Name one
device for producing polarized light. Two polarides are [laced perpendicular to
each other and the transmitted intensity is zero. What happens when one more
Polaroid is placed between these two at an angle of 450?
11.
In
Young’s experiment the width of the fringes obtained with light of wavelength
6000 A0 is 2mm. What will be the fringe width if the apparatus is
immersed in a liquid of refractive index 4/3?
12.
Show
that the maximum intensity in interference pattern is four times the intensity
due to each slit.
13.
In a
single slit diffraction experiment, the width of the slit is made double the
original width. How does this affect the size and intensity of central
diffraction band?
14.
How does
the resolving power of a microscope change on (i) decreasing the wavelength of
light (ii) decreasing the diameter of the objective lens?
15.
Draw the
wavefront for a beam of light (i) coming from a convex lens when a point source
is placed at its focus (ii) divergent radially from a point source.
16.
The
refractive index of a denser medium is 1.732. Calculate (i) Polarising angle of
the medium (ii) angle of refraction.
17.
Determine
the angular separation between the central maximum, and first order maximum of
diffraction pattern due to a single slit of width 0.25mm.
18.
State
two conditions for sustained interference of light. Draw the variation of
intensity with position in Young’s double slit experiment.
19.
State
Huygens principle. For reflection of plane wavefront at a plane reflecting
surface, construct the corresponding reflected wavefront. Using this diagram
prove that angle of incidence is equal to angle of reflection.
20.
Two
independent sources of light cannot be coherent. Why? Two coherent sources have
intensities in the ratio 25:16. Find the ratios of the intensities of maxima to
minima after interference.
21.
In a
single slit diffraction experiment width of the slit is made double the
original width. How does it affect the size and intensity of central
diffraction band? Explain. Draw a graph showing variation of intensity with
angle in single slit diffraction.
22.
What is
meant by plane polarized light. What type of waves show the property of
polarization? Describe a method to produce plane polarized light.
23.
Define
polarizing angle. Derive the relation connecting polarizing angle and
refractive index of the medium.
24.
State
Huygens’s principle. Deduce the laws of refraction on the basis of Huygens’s
principle.
25.
When two
narrow slits 2mm apart are illuminated by a light of wavelength 5000 A0
the third minima is measured to be 0.5mm from the central maxima on a screen.
What is the distance of the screen from the slit?
26.
How does
the resolving power of a microscope change when (i) the wavelength of the light
is increased (ii) the microscope is kept inside water (iii) diameter of the
objective lens is doubled?
27.
In
Young’s double slit experiment when a source of light of wavelength 5000 A0 is
used the fringe width obtained is 0.6cm. If the distance between slit and
screen is reduced to half what would be the wavelength of source to get a 0.003
m wide fringes.
28.
State
the essential condition for diffraction of light to occur. The light of
wavelength 600nm is incident normally on a slit if width 3mm. calculate the
linear width of central maximum when the screen is 3m away from the slit.
29.
Explain
the phenomenon of diffraction of light at a single slit. Show graphically the
variation of intensity with angle in the diffraction pattern. What is meant by
the term angular resolution of a telescope?
30.
What do
you understand by polarization of light? What are plane of polarization and
plane of vibration? Explain polarization (i) by scattering (ii) by reflection.
Explain Young’s
double slit experiment of interference of light waves. Calculate the path
difference between interfering waves and give conditions for maxima and minima.
. Get the expression for dark and bright fringesIMPORTANT QUESTIONS FOR CLASS – X
1. Two
wires of same material are having length L and 2L. Compare their resistance and
resistivity.
2. Why are coils of electric toaster and electric iron made of an alloy rather than a pure metal?
3. Two wires are of same length and radius but one of them is copper and the other is of iron. Which will have more resistance? (Given the resistivity of copper = 1.62 x 10 -8 ohm meter and resistivity of iron = 10 x 10-8 ohm meter.
4. Define 1KWh. Give the relation between 1kwh and Joule.
5. State which has a higher resistance. A 50W or 25W lamp. Also find the ratio of their resistances.
6. A wire of resistance 5 Ohm is spent in the form of closed circle. What is the resistance between 2 points at the ends of any diameter of the circle?
7. Calculate the amount of charge that would flow in one hour through the element of an electric iron drawing a current of 0.4 amps.
8. A electric toaster of resistance 20 Ohm takes a current of 5A. Calculate the heat developed in 30 s.
9. A bulb is rated at 5V, 100mA. Calculate its (1) Power (2) Resistance
10. Name two special characteristics of a heater coil.
2. Why are coils of electric toaster and electric iron made of an alloy rather than a pure metal?
3. Two wires are of same length and radius but one of them is copper and the other is of iron. Which will have more resistance? (Given the resistivity of copper = 1.62 x 10 -8 ohm meter and resistivity of iron = 10 x 10-8 ohm meter.
4. Define 1KWh. Give the relation between 1kwh and Joule.
5. State which has a higher resistance. A 50W or 25W lamp. Also find the ratio of their resistances.
6. A wire of resistance 5 Ohm is spent in the form of closed circle. What is the resistance between 2 points at the ends of any diameter of the circle?
7. Calculate the amount of charge that would flow in one hour through the element of an electric iron drawing a current of 0.4 amps.
8. A electric toaster of resistance 20 Ohm takes a current of 5A. Calculate the heat developed in 30 s.
9. A bulb is rated at 5V, 100mA. Calculate its (1) Power (2) Resistance
10. Name two special characteristics of a heater coil.
Short answer questions (3 marks)
1. Define resistance and resistivity. Give the relation between them. Explain the dependence of resistance on temperature.
2. With the help of neat circuit, derive the expression for the equivalent resistance of 3 resistances connected in series.
3. With the help of neat circuit, derive the expression for the equivalent resistance of 3 resistances connected in parallel
4. (a ) Draw the circuit consisting of a battery of five 2V cells, 5ohm resistor, 10 ohm resistor, 15 ohm resistor and a plug key. All connected in series (b) calculate the current passing through the above circuit when key is closed.
1. Define resistance and resistivity. Give the relation between them. Explain the dependence of resistance on temperature.
2. With the help of neat circuit, derive the expression for the equivalent resistance of 3 resistances connected in series.
3. With the help of neat circuit, derive the expression for the equivalent resistance of 3 resistances connected in parallel
4. (a ) Draw the circuit consisting of a battery of five 2V cells, 5ohm resistor, 10 ohm resistor, 15 ohm resistor and a plug key. All connected in series (b) calculate the current passing through the above circuit when key is closed.
5. Two
identical resistors each of resistance 2 Ohm are connected in turn
(1) in series (2) in parallel
to a battery of 12 V. Calculate the ratio of power consumed in two cases.
6. A piece of wire is redrawn by pulling it until its length is tripled. Compare the new resistance with the original value.
7. An electric kettle is rated 500W, 200V. IT is used to heat 400 gm of water for 30 secs. Assuming the voltage to be 220V calculate the rise in temperature of water. Specific heat capacity of water is 4200 J/Kg ºC.
8. What is the resistance of a copper wire 20 meters long and 0.81 mm in diameter at 20°?
6. A piece of wire is redrawn by pulling it until its length is tripled. Compare the new resistance with the original value.
7. An electric kettle is rated 500W, 200V. IT is used to heat 400 gm of water for 30 secs. Assuming the voltage to be 220V calculate the rise in temperature of water. Specific heat capacity of water is 4200 J/Kg ºC.
8. What is the resistance of a copper wire 20 meters long and 0.81 mm in diameter at 20°?
9. A heater
draws 1100 W at 220V. (a) Find the resistance of the heater (b) Calculate the energy in KWh consumed in a week if the
heater is used daily for 4 hours.
10. The
following three appliances are connected in series to a 120 V house circuit: a
toaster, 1200 W; a coffee pot, 750 W;
and a microwave, 6.0 × 102 W. If all were operated at the same time, what total
current would they draw?
11. Three
resistors with values of 3.0 Ω, 6.0 Ω, and 12 Ω are connected in series. What
is the equivalent resistance
of this combination?
12. Three
resistors with values of 4.0 Ω, 6.0 Ω, and 10.0 Ω are connected in parallel.
What is their equivalent
resistance?
13. Two
resistors with values of 6.0 Ω and 12 Ω are connected in parallel. This
combination is connected in
series with a 4.0 Ω resistor. What is the overall resistance of this combination?
14. A circuit
contains a 1.5 volt battery and a bulb with a resistance of 3 ohms. Calculate
the current.
15. Two
resistors with values of 6.0 Ω and 12 Ω are connected in parallel. This
combination is connected in
Series with a 2.0 Ω resistor and a 24 V battery. What is the current in the 2.0 Ω resistor?
16. What is
the equivalent resistance for the resistors in the figure below?
17. What is the equivalent resistance for the resistors in the figure below?
18. For the circuit shown below find the following,
17. What is the equivalent resistance for the resistors in the figure below?
18. For the circuit shown below find the following,
a. What is the equivalent resistance for the resistors in
the figure below?
b. What is the total voltage drop across the entire below
circuit?
1. State Ohms law with a neat circuit. Explain how this law can be verified and also plot the expected v-I graph.
2. (a) Differentiate resistance and resistivity
(b) the ratio of resistivities of two materials a and b is 1:2, ratio of their length is 3:4 and if the ratio of radii is 2:3 find the ratio of resistance of a and b.
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