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Biology; Chemistry; Physics: Post your doubts here!

iamLbert

iamLbert

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Saad Mughal said:
(a) The power is given in Watts so convert the time to Seconds.
Time = 2 * 60 = 120 s.
Power = Energy/Time,
Energy = Power * Time
Energy = 85 * 120
Energy = 10200 J

(b) Specific Latent Heat = Energy Supplied/Mass
Specific Latent Heat = 10200/31
Specific Latent Heat = 329.0 J/g (3 sig. fig.)

(c) This is because the energy required to heat the ice to 0 deg. C is also to be taken into account and hence, the energy supplied for 'melting' the ice would be less in the first 2 minutes.
Click to expand...
So for latent heat, the formula is Q = m*c and for time have to be aligned to seconds?
 
iamLbert

iamLbert

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danial 234

danial 234

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In 23, as the stud should prevent the armature from being attracted too strongly so it should be a non magnetic material copper. Rest should be iron
 
iamLbert

iamLbert

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Amnaa said:
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s03_qp_1.pdf
guyz please explain me Question no. 4 , 6 , 16, 23. 31, 34, 37, 38 and 40.
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Can the others then explain 6, 23, 34, and 40? For Amnaa, question 38 uses the formula of 1 / 2^(time asked/half-life), then for question 37 is alpha-particle since alpha-particle have 2 proton and 2 neutron.
dcmcur.gif
Question 31
 
Saad Mughal

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Amnaa said:
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s03_qp_1.pdf
guyz please explain me Question no. 4 , 6 , 16, 23. 31, 34, 37, 38 and 40.
Click to expand...

4. Density = Mass/Volume.
Density = 27/30
Density = 0.9 g/cm3.

6. The mass is in a state of rest so resultant force = 0.

16, Look, a thick wall means that the glass will not reach the surrounding temperature properly, which means that there will be unequal expansion. So to prevent this, we will use a thin wall, now, if it expands greatly on heating than the rise in temperature will cause it to break so the best option should be thin and expands little.

23, Iron is easily magnetized and copper is a non-magnetic material. M and L should be iron (so that they are magnetized easily by a current and other magnet), whereas S (since it stops the armature from being attracted) should be a non-magnetic material which is only copper in the choices.

31, They've asked for D.C. motor and it's a commutator (split ring commutator) that reverses the direction of current to ensure a uniform rotation of the wire.

34, An alternating current is induced since the magnet moves to and fro (that is forward and magnet) and from Fleming's Right Hand Rule we can tell that the current induced is in opposite direction each time so the graph of alternating current would be there. The graph of alternating current is a COSINE graph so option A should be correct.

37, Well, this is easy, we bombard the Uranium - 235 atom with neutrons to make it unstable and cause a fission reaction so C should be the answer.

38, Well, A is incorrect, and so is B, Half life means that after x minutes the isotope would have become HALF be decaying; D is also wrong because after 2 minutes the CURRENT half life would turn half, so after 4 minutes, the isotope would be (1/2)^2 = 1/4 of the original.

40, Well, it's A because the experiment observed the concentrated mass of a Nuclei; this is a fact.
 
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