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  1. J

    Heat radiation and photons

    Homework Statement Homework Equations The Attempt at a Solution No . The number of photons should decrease . As the rate of heat transfer decreases with time , the net electromagnetic radiation from the hot body to the surroundings decrease . Heat radiations are composed of photons ...
  2. J

    MCQ : Comparing characteristics of two photons

    Homework Statement Homework Equations The Attempt at a Solution I am surely making some very silly mistake in this problem . Presuming linear momenta means magnitude of momentum , to me all four options look correct . a) since wavelengths are same , energy is same which means momentum...
  3. J

    De Broglie wavelength of electron and proton

    Homework Statement Homework Equations The Attempt at a Solution de Broglie wavelength λ of a particle = h /P a) since mass of proton is more than electron and speed is same , momentum of proton is more . De Broglie wavelength of proton will be less . b) wavelengths will be same . c)...
  4. J

    Is this question on Intensity of light from Sun correct?

    Homework Statement Homework Equations The Attempt at a Solution This is an example given in the book . But I am just wondering whether the question itself is correct . How can intensity of light emitted from Sun is given a constant ? Shouldn't 1400 be the power emitted from Sun ? If...
  5. J

    Comparing self inductance of three solenoids

    Homework Statement Homework Equations The Attempt at a Solution Self inductance depends on the geometry of the solenoid . It doesn't depend on the sense of windings . So , L1 = L2 . But I don't understand how to deal with superconducting wires . Does a superconducting wire affect the...
  6. J

    Magnetic field and coplanar loops

    Homework Statement Homework Equations The Attempt at a Solution The current in the inner loop should flow in anticlockwise direction so as to resist the increase in flux of the external magnetic field . But how do I deal with the outer loop since there is smaller loop inside it ? I...
  7. J

    LR circuit - Which bulb gets dim quickly?

    Homework Statement Homework Equations The Attempt at a Solution When the switch is off , the current in the inductor doesn't drop to zero instantaneously . The current in the loop consisting of inductor , resistor and two bulbs will decay gradually . Now since there is a complete circuit...
  8. J

    Magnetic field and metal box

    Homework Statement Homework Equations The Attempt at a Solution I have honestly no idea about this concept . Book doesn't mention anything about this . This looks similar to Faraday cage in electrostatics . But I don't understand how this works in case of magnetic fields . Is this related...
  9. J

    Self inductance of a solenoid

    Homework Statement Homework Equations The Attempt at a Solution Self inductance L = μ0n2πr2l . This means it depends only on geometrical factors . So , self inductance in both the cases should be equal . But if I think in terms of L = Φ/I , then Magnetic field at the center is twice...
  10. J

    Direction of induced current in the loop

    Homework Statement Homework Equations The Attempt at a Solution I am having a little doubt as to how to think of the moving electron as a current . I am considering the moving electron as a very tiny (infinitesimal ) current element . It is as if when the electron is at A , there is a...
  11. J

    Magnet moved in a circular coil

    Homework Statement Homework Equations The Attempt at a Solution As the magnet moves in and out of the coil , flux linked with the coil changes , as a result an EMF is induced in the coil . A current flows in the coil . The current depends on how fast the magnet is moved . Current will vary...
  12. J

    Magnetic field due to a solenoid

    Homework Statement Homework Equations The Attempt at a Solution I am having trouble interpreting the language of the problem statement . What does it mean that "half number of turns are wound " ? When the solenoid is cut , the length becomes 1/4th of the original and number of turns also...
  13. J

    Photoelectric current and a convex lens

    Homework Statement Homework Equations The Attempt at a Solution The photoelectric current is directly proportional to the intensity of the light falling on it . It will not depend on the focal length of the lens . When the lens of half the diameter is used , intensity is halved . This...
  14. J

    Bar magnet and a current carrying wire

    Homework Statement Homework Equations The Attempt at a Solution The magnetic field lines due to the infinite wire will be clockwise .When P is the midpoint of the magnet , Magnetic field at the South Pole will have a component upwards and a component towards right .This means S will...
  15. J

    Excess pressure inside a soap bubble

    Homework Statement Homework Equations The Attempt at a Solution Excess pressure inside a spherical soap bubble is 4S/R . How to deal with the cylindrical shape ? Why does the question specify it to be "long" ?
  16. J

    Force between the plates of a charged capacitor

    Homework Statement Homework Equations The Attempt at a Solution Force between capacitor plates is Q2/(2Aε0) . If the distance between the plates is small as compared to the area , then force between the plates does not depend on the distance . But I am not sure how to deal with this...
  17. J

    Find mass of a rope pulled by a force

    Homework Statement Homework Equations The Attempt at a Solution The force F exerted by the wall on the left end of the rope will make an angle 30° with the vertical . If we do the force balance , F sin30° = 20 Fcos30° = Mg This gives M = 2√3 Kg . This gives 3.5 Kg . But answer given is...
  18. J

    Induced EMF and current in the circuit

    Homework Statement Homework Equations The Attempt at a Solution First I will label a few points . A is the point on the ring touching the rails , vertically below P . B is the point on the ring touching the rails , vertically below Q . T is the topmost point on the ring . M is the...
  19. J

    Current flowing in a branch in a circuit

    Homework Statement Homework Equations The Attempt at a Solution For calculation sake I will consider R = 1Ω . Final answer will be in mA instead of A . The middle two resistors 3R and 4R are in parallel , so I consider their equivalent resistance 12R/7 in the middle branch . In the left...
  20. J

    Speed of escaping gas from a cylinder

    Homework Statement Homework Equations The Attempt at a Solution I don't understand which concept to apply in this question . The hint says to apply Bernoulli's equation and uses ∆P (excess pressure ) = (1/2) ρ v2 . This does give right answer . But I think this is wrong . We cannot apply...
  21. J

    Coefficient of volume expansion of gas

    Homework Statement Homework Equations The Attempt at a Solution Coefficient of volume expansion γ = ∆V/V∆T VT2 = constant Differentiating we get , T2∆V + 2VT∆T = 0 ∆V/V∆T = -2/T So , option 2) looks right . Is that correct ? How do I interpret the answer ? Does that mean the...
  22. J

    Two parallel diodes in a circuit

    Homework Statement Homework Equations The Attempt at a Solution I am not quite sure how to deal with the two diodes in parallel . How do we know what is the potential applied across the two diodes so as to decide which one is conducting ?
  23. J

    Optics: Image formed from a glass block

    Homework Statement Homework Equations The Attempt at a Solution I have solved this problem . For that I had to use refraction at the first surface , then reflection from the back side and then again refraction from the first surface . This gives me the correct answer . But when I saw...
  24. J

    Is there a quicker way to solve this projectile problem?

    Homework Statement Homework Equations The Attempt at a Solution I solved this problem and got the correct answer 108 m . But I had to solve a DE . This question is from a test where we get around 1 minute to solve a problem . I took half an hour to solve it :wideeyed: . It looks like a...
  25. J

    Current flowing in the middle branch -- Why 2 different answers?

    Homework Statement Homework Equations The Attempt at a Solution The two batteries are in series in both the left and right branch .This means the potential difference applied across the two middle resistors is 20 V .Hence the current flowing through them is 20/10= 2 A . This is indeed the...
  26. J

    Inertial and Gravitational mass - Assertion Reason

    Homework Statement [/B] Homework Equations The Attempt at a Solution I think the two masses , inertial and gravitational are equivalent and because of this fact , the ratio of the two masses is one . The correct option should be 1) . But the answer given is 3) i.e A statement is true and...
  27. J

    Law of gravitation MCQ

    Homework Statement Homework Equations The Attempt at a Solution I think if the law of gravitation changes then the law of areas should still hold .Law of areas is nothing but law of conservation of angular momentum . Since the changed law of gravitation is still central the law of areas...
  28. J

    Pressure in the vessel containing water

    Homework Statement Homework Equations The Attempt at a Solution I think the pressure that the question is relating is the vapour pressure but I do not understand how that depends on the volume of the water contained in the vessel .Is there a relationship between the two ?
  29. J

    Sphere dipped in water

    Homework Statement Homework Equations The Attempt at a Solution There can be two cases 1) The sphere might be a shell such that it floats on the water .When the temperature increases , even though density of water decreases , the force of buoyancy should remain same . Because force of...
  30. J

    Equivalent resistance between two points

    Homework Statement Homework Equations The Attempt at a Solution From symmetry , C and D are at the same potential . So , resistance between them can be removed . This leaves us with three parallel branches between A and B i.e 45 Ω || 45 Ω || 15Ω . The net resistance will be 9 Ω . But...
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