Hi All
We receive lot of entries for the contest.Thanks all for the Response
Answer to the questions are
1. c
2.a
3.b,c
4.b
5.a
The winner of the contest is Indranil Chakraborty from Mussoorie, Uttarakhand
He will soon recieve the stationary Gift worth RS 200
Congratutlation!!!!!!!!!!!!!
Thanks to all for overwhelming response!!!!!
Saturday, 27 September 2008
Friday, 19 September 2008
IITJEE PHYSICS:Current Electricity Part -I
Agenda: Summary of Current Electricity
Some basic point about Electricty
-A current flows along a metal or wire when battery is connected to it.
-Current in a wire is due to free electrons moving along the wire
-The Battery has a Potential difference between its poles due to chemical changes inside the battery.The Potential difference pushes the electrons alongs the metal.The Potential diffrence between the terminal is call the EMF of the battery.
-One pole of the battery is called positive pole and another one is call the negative pole.
-Current direction is opposite to the electron flow direction.
-EMF is measured in Volt
Electric current is defined as the rate at which charge flows inside the conductor
so
I=Q/t
- Its unit is Amphere
Also I=dQ/dt
Drift speed of electrons inside the conductor
vd=I/neA
Where I is the current,n is the number of the electron per unit volume ,e is the electronic charge and A is the area of the crossection of the conductor
Ohms Law
V=IR
where V is the Potential difference accross its ends
I is the current flow
And R is the electrical Resistance of the conductor.Electrical Resistance unit is Ohm
ELectrical Resistivity
It is defined as
ρ=RA/L
Where R is the Resistance
A is the crossectional Area
L is the length
Series Resistors
R=R1+R2+R3
Parallel Resistors
(1/R)=(1/R1)+(1/R2)+(1/R2)
Terminal Voltage of the Cell
V=E-Ir
where E is the EMF of the cell and r is the internal resistance of the Cell
Please let us know if you like this post and what can be done to improve on that
Please comments
Some basic point about Electricty
-A current flows along a metal or wire when battery is connected to it.
-Current in a wire is due to free electrons moving along the wire
-The Battery has a Potential difference between its poles due to chemical changes inside the battery.The Potential difference pushes the electrons alongs the metal.The Potential diffrence between the terminal is call the EMF of the battery.
-One pole of the battery is called positive pole and another one is call the negative pole.
-Current direction is opposite to the electron flow direction.
-EMF is measured in Volt
Electric current is defined as the rate at which charge flows inside the conductor
so
I=Q/t
- Its unit is Amphere
Also I=dQ/dt
Drift speed of electrons inside the conductor
vd=I/neA
Where I is the current,n is the number of the electron per unit volume ,e is the electronic charge and A is the area of the crossection of the conductor
Ohms Law
V=IR
where V is the Potential difference accross its ends
I is the current flow
And R is the electrical Resistance of the conductor.Electrical Resistance unit is Ohm
ELectrical Resistivity
It is defined as
ρ=RA/L
Where R is the Resistance
A is the crossectional Area
L is the length
Series Resistors
R=R1+R2+R3
Parallel Resistors
(1/R)=(1/R1)+(1/R2)+(1/R2)
Terminal Voltage of the Cell
V=E-Ir
where E is the EMF of the cell and r is the internal resistance of the Cell
Please let us know if you like this post and what can be done to improve on that
Please comments
Wednesday, 3 September 2008
Physics for IITJEE:Exercise your Brain with Miscellaneous Physics Question
Question 1:
A 2 kg body moving to the right with speed 6 m/s coliides elastcally with a stationary body of mass 4 kg.
a.Find the velocity vector of each mass relative to center of mass before and after the collsion
b.Find the velocity vector of the each mass in original frame after the collision
c.How much energy was transfered to the 4 kg body.
Take i as the unit vector in the right direction
Answer
a.
Before collision
Velocity vector of mass 2 kg=4i m/s
Velocity vector of mass 4 kg=-2i m/s
After collision
Velocity vector of mass 2 kg=-4i m/s
Velocity vector of mass 4 kg=2i m/s
b
Velocity vector of mass 2 kg=-2i m/s
Velocity vector of mass 4 kg=4i m/s
c. 32 J
Hints:
Velocity of the center of mass=m1v1+m2v2/m1+m2
Velocity w.r.t CM=v-vcm
Applying law of linear momentum and energy conservation,veloclities after collosion could be find out
Question 2:
A small solid cylinder of radius r rolls down from the top of sphere of Radius R without slipping.
a. find the angle made from the vertical at which the cylinder loses contact with the surface of the sphere
b.find the angular velocity of the cylinder at the moment it loses contact with the surface of the sphere
Answer
a. cos-1(4/7)
b.(2/r)[(R+r)g/7]1/2
hints:
Normal reaction will become zero at the point of losing contact
so centripetal force will become equal to the weight components across the radius.
Also applying law of conservation of energy ...we can find the solution
Question 3:
An gas obeys Vander waal equation
(P+a/V2)(V-b)=nRT
Find following for such a gas
A. The dimensional formula for constant a is
a.ML5T-2
b.ML5T-1
c.ML-1T-1
d. M0L-0T0
B. Find the workdone by this gas when gas expand from V to 2V at constant temperature T
a.nRTloge(2V-b/V-b) -a/V
b.nRTloge(2V-b/V-b) +a/V
c. nRTloge(2V-b/V-b)
d. none of the above
C.Bulk modulus at constant pressure is defined as
K=(-1/V)(dP/dV)T
Find the value of k for this gas
a.(1-b/V)(p-a/V2+2a/V3)
b. (1+b/V)(p-a/V2+2a/V3)
c.(1-b/V)(p-a/V2-2a/V3)
d.None of the above
Answer:
A.ML5T-2
B.nRTloge(2V-b/V-b) -a/V
Question 4:
An electron (mass m and charge e) is moving along the axis of the ring of radius r and carrying a charge q.Find the time period of small oscillation of the electron about the center of the ring
Answer
T=4π(πε0mr3/eq)1/2
Hint:
Electric field at a point on the axis of the ring at the distance x from its center is
E=qx/4πε0(r2+x2)3/2
A 2 kg body moving to the right with speed 6 m/s coliides elastcally with a stationary body of mass 4 kg.
a.Find the velocity vector of each mass relative to center of mass before and after the collsion
b.Find the velocity vector of the each mass in original frame after the collision
c.How much energy was transfered to the 4 kg body.
Take i as the unit vector in the right direction
Answer
a.
Before collision
Velocity vector of mass 2 kg=4i m/s
Velocity vector of mass 4 kg=-2i m/s
After collision
Velocity vector of mass 2 kg=-4i m/s
Velocity vector of mass 4 kg=2i m/s
b
Velocity vector of mass 2 kg=-2i m/s
Velocity vector of mass 4 kg=4i m/s
c. 32 J
Hints:
Velocity of the center of mass=m1v1+m2v2/m1+m2
Velocity w.r.t CM=v-vcm
Applying law of linear momentum and energy conservation,veloclities after collosion could be find out
Question 2:
A small solid cylinder of radius r rolls down from the top of sphere of Radius R without slipping.
a. find the angle made from the vertical at which the cylinder loses contact with the surface of the sphere
b.find the angular velocity of the cylinder at the moment it loses contact with the surface of the sphere
Answer
a. cos-1(4/7)
b.(2/r)[(R+r)g/7]1/2
hints:
Normal reaction will become zero at the point of losing contact
so centripetal force will become equal to the weight components across the radius.
Also applying law of conservation of energy ...we can find the solution
Question 3:
An gas obeys Vander waal equation
(P+a/V2)(V-b)=nRT
Find following for such a gas
A. The dimensional formula for constant a is
a.ML5T-2
b.ML5T-1
c.ML-1T-1
d. M0L-0T0
B. Find the workdone by this gas when gas expand from V to 2V at constant temperature T
a.nRTloge(2V-b/V-b) -a/V
b.nRTloge(2V-b/V-b) +a/V
c. nRTloge(2V-b/V-b)
d. none of the above
C.Bulk modulus at constant pressure is defined as
K=(-1/V)(dP/dV)T
Find the value of k for this gas
a.(1-b/V)(p-a/V2+2a/V3)
b. (1+b/V)(p-a/V2+2a/V3)
c.(1-b/V)(p-a/V2-2a/V3)
d.None of the above
Answer:
A.ML5T-2
B.nRTloge(2V-b/V-b) -a/V
Question 4:
An electron (mass m and charge e) is moving along the axis of the ring of radius r and carrying a charge q.Find the time period of small oscillation of the electron about the center of the ring
Answer
T=4π(πε0mr3/eq)1/2
Hint:
Electric field at a point on the axis of the ring at the distance x from its center is
E=qx/4πε0(r2+x2)3/2
Monday, 25 August 2008
IITJEE Test series 2 (Modern Physics)
(A) Multiple choice questions with one answer
1. The ionizing power of the radiations are in the increasing order of
(a) γ,β ,α
(b) α , β,γ
(c) α , γ,β
(d) β, γ,α
2.A photon of energy 5.0 eV imparts all it's energy to an electron that leaves a metal surface with 1.5 eV of kinetic energy.The work function α of metal would be
(a) 6.5 eV
(b) 3.5 eV
(c) 3.9 eV
(d) 1.5 eV
3. A thermal neutron of mass 1.67× 10-27 Kg is travelling at a speed of 2500 m/s. de Brogli wavelength of thermal neutron is
(a) 1.4 × 10-10m
(b) 12 × 10-10m
(c) 1.6 × 10-10m
(d) 1.0 × 10-10m
4. Uncertainity in the position of a particle is equal to twice its de Brogli wavelength. Uncertainity in its velocity would be
(a) Δvx≥(1/4π)vx
(b) Δvx≥(1/π)vx
(c) Δvx≥(1/2π)vx
(d) Δvx≥(1/8π)vx
5. The shortest wavelength of X-Rays emitted from an X-Ray tube depends upon
(a) atomic number of target material
(b) current in the tube
(c) voltage applied to the tube
(d) nature of gas in the tube
6. The largest wavelength present in the Balmer series of hydrogen atom is
(a) 656 nm
(b) 500 nm
(c) 600 nm
(d) 756 nm
(B) Matrix match type
Match the list P with the list Q to name the series for quantum jump of electrons in hydrogen atom
list P
(a) n=2 to n=3
(b) n=3 to n=4
(c) n=4 to n=5
(d) n=5 to n=6
list Q
1. Balmer
2. lyman
3. Paschen
4. Brackett
5. Pfund
Answers
(A) Multiple choice questions with one answer
1. a
2. b
3. c
4. d
5. c
6. d
(B) Matrix match type
a-2
b-1
c-3
d-4
1. The ionizing power of the radiations are in the increasing order of
(a) γ,β ,α
(b) α , β,γ
(c) α , γ,β
(d) β, γ,α
2.A photon of energy 5.0 eV imparts all it's energy to an electron that leaves a metal surface with 1.5 eV of kinetic energy.The work function α of metal would be
(a) 6.5 eV
(b) 3.5 eV
(c) 3.9 eV
(d) 1.5 eV
3. A thermal neutron of mass 1.67× 10-27 Kg is travelling at a speed of 2500 m/s. de Brogli wavelength of thermal neutron is
(a) 1.4 × 10-10m
(b) 12 × 10-10m
(c) 1.6 × 10-10m
(d) 1.0 × 10-10m
4. Uncertainity in the position of a particle is equal to twice its de Brogli wavelength. Uncertainity in its velocity would be
(a) Δvx≥(1/4π)vx
(b) Δvx≥(1/π)vx
(c) Δvx≥(1/2π)vx
(d) Δvx≥(1/8π)vx
5. The shortest wavelength of X-Rays emitted from an X-Ray tube depends upon
(a) atomic number of target material
(b) current in the tube
(c) voltage applied to the tube
(d) nature of gas in the tube
6. The largest wavelength present in the Balmer series of hydrogen atom is
(a) 656 nm
(b) 500 nm
(c) 600 nm
(d) 756 nm
(B) Matrix match type
Match the list P with the list Q to name the series for quantum jump of electrons in hydrogen atom
list P
(a) n=2 to n=3
(b) n=3 to n=4
(c) n=4 to n=5
(d) n=5 to n=6
list Q
1. Balmer
2. lyman
3. Paschen
4. Brackett
5. Pfund
Answers
(A) Multiple choice questions with one answer
1. a
2. b
3. c
4. d
5. c
6. d
(B) Matrix match type
a-2
b-1
c-3
d-4
Thursday, 21 August 2008
Modern Physics Test Series
(A) Multple choice questions
1. Photoelectric emission takes place when
(a)electrons falls on photosensitive surface
(b)alpha particles falls on photosensitive surface
(c)light rays falls on photosensitive surface
(d)neutrons falls on photosensitive surface
2. The velocity of most energetic photo electrons emitted from metal surface depends on
(a) time for which radiation fall on metal surface
(b) the frequency of incident light
(c) the intensity of incident light
(d) none of the above
3. The work funcion of a metal is w and λ is the wavelength of incident radiation. there would be no emission of photoelectrons when
(a) λ > hc/w
(b) λ < hc/w
(c) λ = hc/w
(d) λ ≤ hc/w
4. The fact that was not inferred from the Rutherford model of the atom was that the
(a) nucleus occupied a small space inside the atom
(b) nucleus consisted of neutrons and protons
(c) electrons were outside the nucleus of the atom
(d) nucleus was dense in nature
5. A graph showing the energy of the photoelectron as a fuction of the frequency of the radiation for a given emitting surface is best represented as
(a)
(b)
(c)
(d)
(B) Matrix match type question
6. Match the items mentioned with those given in group (P) with those given in group (Q)
(P)
(a) The concept of nuclear atom was
established from the experiment on the
(b) Wave aspect of matter was confirmed by
(c) Bohr theory was successful in explaining
(d) Photons may cause
(Q)
(1) emission of electrons from the metal surface
(2) scattering of alpha particles by a gold foil
(3) diffraction of electrons by a crystal
(4) bright line spectra of hydrogen atom
(5) scattering of X-rays by electrons
Answers
1. (c)
2. (b)
3. (a)
4. (c)
5. (a)
6. a-2
b-3
c-4
d-1
1. Photoelectric emission takes place when
(a)electrons falls on photosensitive surface
(b)alpha particles falls on photosensitive surface
(c)light rays falls on photosensitive surface
(d)neutrons falls on photosensitive surface
2. The velocity of most energetic photo electrons emitted from metal surface depends on
(a) time for which radiation fall on metal surface
(b) the frequency of incident light
(c) the intensity of incident light
(d) none of the above
3. The work funcion of a metal is w and λ is the wavelength of incident radiation. there would be no emission of photoelectrons when
(a) λ > hc/w
(b) λ < hc/w
(c) λ = hc/w
(d) λ ≤ hc/w
4. The fact that was not inferred from the Rutherford model of the atom was that the
(a) nucleus occupied a small space inside the atom
(b) nucleus consisted of neutrons and protons
(c) electrons were outside the nucleus of the atom
(d) nucleus was dense in nature
5. A graph showing the energy of the photoelectron as a fuction of the frequency of the radiation for a given emitting surface is best represented as
(a)
(b)
(c)
(d)
(B) Matrix match type question
6. Match the items mentioned with those given in group (P) with those given in group (Q)
(P)
(a) The concept of nuclear atom was
established from the experiment on the
(b) Wave aspect of matter was confirmed by
(c) Bohr theory was successful in explaining
(d) Photons may cause
(Q)
(1) emission of electrons from the metal surface
(2) scattering of alpha particles by a gold foil
(3) diffraction of electrons by a crystal
(4) bright line spectra of hydrogen atom
(5) scattering of X-rays by electrons
Answers
1. (c)
2. (b)
3. (a)
4. (c)
5. (a)
6. a-2
b-3
c-4
d-1
Wednesday, 13 August 2008
IITJEE PHYSICS: Mechanics
Mulitiple choice question with one or more answer
1. The motion of center of mass of a system of two particles is unaffected by their internal forces
a, irrespective of the actual direction of the internal forces
b,only if they are along the line joining the particles
c.only if they are obliquely inclined to the line joinng the particles
d. only if they are right angles to the line joining the particles
2.Two discs of moments of inertia I1 and I2 about their respective axis rotating with angular frequencies ω1 and ω2 respectively are brought into contact face to face with their axes of rotation coincident.Which of the following is true
a.The angular frequency of the composite disc is (I1ω1+I2ω2)/(I1+I2)
b.dL/dt is constant for the system
c.Moment of the inertia of the composite disc about the axis is I1+I2
d. None of these
3.Net force on a system of particles is zero from some interial frame.which of the following is correct
a.Center of mass acceleration is zero from that inertial frame
b. Net momentum is constant from that frame
c.Net momentum from the frame of Center of mass is zero and constant
d. KE of the system from center of mass frame may be constant
4.Three points masses each of mass m are placed at the corner of an equilateral triangle of side a.The moment of inertia of the system about an axis along one side of an triangle is
a.3ma2/4
b. ma2/4
c. ma2/2
d ma2/6
5. A solid sphere rolls without slipping with speed v and presses a spring of spring constant k.The compression in the spring will be
a.(2Mv2/3k)1/2
b.(2Mv2/5k)1/2
c.(5kv2/7M)1/2
d.(7Mv2/5k)1/2
6.A solid cylinder of mass M and radius R is being pulled along a horizontal surface on which its perform pure rolling by a horizontal force F applied at its center.which of the following is true
a.Angular acceleration of the cylinder about the axis passing through center of mass is 2F/3MR
b.Frictional force acting on the cylinder is F/3
c.Velocity of a point on the top of cylinder after 3 sec is 4P/M
d . None of these
7.A uniform chain of mass M and lenght L is held on a horizontal frictionless table with 1/k lenght hanging over the edge of the table.The workdone in pulling the chain up the table
a.MgL/k
b. MgL/2k
c. MgL/k2
d. MgL/2k2
Solutions
1.Ans a
2.Ans a,b,c
3.ans a,b,c,d
4.aNS A
6.ans a,b,c
7.ans d
1. The motion of center of mass of a system of two particles is unaffected by their internal forces
a, irrespective of the actual direction of the internal forces
b,only if they are along the line joining the particles
c.only if they are obliquely inclined to the line joinng the particles
d. only if they are right angles to the line joining the particles
2.Two discs of moments of inertia I1 and I2 about their respective axis rotating with angular frequencies ω1 and ω2 respectively are brought into contact face to face with their axes of rotation coincident.Which of the following is true
a.The angular frequency of the composite disc is (I1ω1+I2ω2)/(I1+I2)
b.dL/dt is constant for the system
c.Moment of the inertia of the composite disc about the axis is I1+I2
d. None of these
3.Net force on a system of particles is zero from some interial frame.which of the following is correct
a.Center of mass acceleration is zero from that inertial frame
b. Net momentum is constant from that frame
c.Net momentum from the frame of Center of mass is zero and constant
d. KE of the system from center of mass frame may be constant
4.Three points masses each of mass m are placed at the corner of an equilateral triangle of side a.The moment of inertia of the system about an axis along one side of an triangle is
a.3ma2/4
b. ma2/4
c. ma2/2
d ma2/6
5. A solid sphere rolls without slipping with speed v and presses a spring of spring constant k.The compression in the spring will be
a.(2Mv2/3k)1/2
b.(2Mv2/5k)1/2
c.(5kv2/7M)1/2
d.(7Mv2/5k)1/2
6.A solid cylinder of mass M and radius R is being pulled along a horizontal surface on which its perform pure rolling by a horizontal force F applied at its center.which of the following is true
a.Angular acceleration of the cylinder about the axis passing through center of mass is 2F/3MR
b.Frictional force acting on the cylinder is F/3
c.Velocity of a point on the top of cylinder after 3 sec is 4P/M
d . None of these
7.A uniform chain of mass M and lenght L is held on a horizontal frictionless table with 1/k lenght hanging over the edge of the table.The workdone in pulling the chain up the table
a.MgL/k
b. MgL/2k
c. MgL/k2
d. MgL/2k2
Solutions
1.Ans a
2.Ans a,b,c
3.ans a,b,c,d
4.aNS A
6.ans a,b,c
7.ans d
Monday, 11 August 2008
Current electricity test series
(A) Assertion reason type question.
(a) If both assertion and reason are true and reason is correct explaination of assertion.
(b) If both assertion and reason are true and reason is not correct explaination of assertion.
(c) Assertion is true but reason is false.
(d) both assertion and reason are false.
(1)
Assertion:Wire carrying current is not charged.
Reason:It is because , at any instant number of electrons leaving wire is sometimes equal to the number of electrons flowing in from the battery.
(2)
Assertion:Drift velocity of electrons decreases on increasing temperature of the conductor.
Reason:It is because, on increasing temperature of a conductor , the value of resistivity of it's material increases.
(3)
Assertion:Resistors are connected in series combination in order to increase the resistance of the circuit.
Reason:In series combination potential difference across any resistor is proportional to it's resistance.
(4)
Assertion:A potentiometer measures the potential difference more accurately then a voltmeter.
Reason:Because it has a wire of high resistance and draws a heavy current from external circuit.
(B) Multiple choice questions with only one answer
(5) A constant voltage is applied between the two ends of a uniform metalic wire and some heat is developed in it . The heat developed is doubled if,
(a) both length and radius of wire are halved
(b) both length and radius of wire are doubled
(c) radius of wire is doubled
(d) length of wire is doubled
(6) Kirchoff's first law of electric circuits is based on the law of conservation of
(a) only on mass
(b) only on charge
(c) on charge as well as on energy
(d) on charge as well as on mass
(7)The temperature coefficent of resistance of wire is 0.00125°C-1. At 300K, it's resistance is 1 ohm. The resistance of wire would be 2 ohm at
(a) 1154K
(b) 1127K
(c) 1167K
(d) 1176K
(8) If the length of the potentiometer wire is increased, then the accuracy in determination of null point
(a) will increase
(b) will decrease
(c) will remain unaffected
(d) can not be decided , untill emf of auxiliary battery is known
(9) Each of the resistance in the network shown in the figure is equal to R. The resistance between terminal A and B is
(a) R
(b) 5R
(c) 3R
(d) 6R
(10)The current voltage graph for a given metallic wire at two different temperatures T1 and T2 are shown in the fig. which one of the following option is true
(a) T1 = T2
(b) T1 < T2
(c) T1 > T2
(d) none of the above
Solutions
1.c
2.a
3.b
4.c
5.b
6.b
7.b
8.a
9.a
10.b
(a) If both assertion and reason are true and reason is correct explaination of assertion.
(b) If both assertion and reason are true and reason is not correct explaination of assertion.
(c) Assertion is true but reason is false.
(d) both assertion and reason are false.
(1)
Assertion:Wire carrying current is not charged.
Reason:It is because , at any instant number of electrons leaving wire is sometimes equal to the number of electrons flowing in from the battery.
(2)
Assertion:Drift velocity of electrons decreases on increasing temperature of the conductor.
Reason:It is because, on increasing temperature of a conductor , the value of resistivity of it's material increases.
(3)
Assertion:Resistors are connected in series combination in order to increase the resistance of the circuit.
Reason:In series combination potential difference across any resistor is proportional to it's resistance.
(4)
Assertion:A potentiometer measures the potential difference more accurately then a voltmeter.
Reason:Because it has a wire of high resistance and draws a heavy current from external circuit.
(B) Multiple choice questions with only one answer
(5) A constant voltage is applied between the two ends of a uniform metalic wire and some heat is developed in it . The heat developed is doubled if,
(a) both length and radius of wire are halved
(b) both length and radius of wire are doubled
(c) radius of wire is doubled
(d) length of wire is doubled
(6) Kirchoff's first law of electric circuits is based on the law of conservation of
(a) only on mass
(b) only on charge
(c) on charge as well as on energy
(d) on charge as well as on mass
(7)The temperature coefficent of resistance of wire is 0.00125°C-1. At 300K, it's resistance is 1 ohm. The resistance of wire would be 2 ohm at
(a) 1154K
(b) 1127K
(c) 1167K
(d) 1176K
(8) If the length of the potentiometer wire is increased, then the accuracy in determination of null point
(a) will increase
(b) will decrease
(c) will remain unaffected
(d) can not be decided , untill emf of auxiliary battery is known
(9) Each of the resistance in the network shown in the figure is equal to R. The resistance between terminal A and B is
(a) R
(b) 5R
(c) 3R
(d) 6R
(10)The current voltage graph for a given metallic wire at two different temperatures T1 and T2 are shown in the fig. which one of the following option is true
(a) T1 = T2
(b) T1 < T2
(c) T1 > T2
(d) none of the above
Solutions
1.c
2.a
3.b
4.c
5.b
6.b
7.b
8.a
9.a
10.b
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