HiggsHunter Posted September 15, 2012 Report Share Posted September 15, 2012 If the waves have less speed in medium B, shouldn't they be refracted towards the normal?Thanks for answering!Yes, the direction of motion of the waves is refracted towards the normal as the waves slow down on entering the region B of shallower water. That is why ocean waves often arrive almost perpendicularly to the shore, even though they are travelling at a different angle to the shoreline further out to sea. Reply Link to post Share on other sites More sharing options...
IB-Adam Posted September 15, 2012 Report Share Posted September 15, 2012 (edited) Hey another question:I was wondering, why are the waves slower in shallow water? Shouldn't it be the opposite as it is a less dense medium? And would the wavefronts be refracted away from the normal?Thank you!I don't know about the shallow water thing but I can tell you that shallower water doesn't make it less or more dense, it's still water The little lines you have drawn are correct if that's what you were asking and I believe those are away from the normal. The straight arrow that runs through the waves in region A is the normal and the waves you have slightly drawn in region B redirect away from it.If the waves have less speed in medium B, shouldn't they be refracted towards the normal?Thanks for answering!Yes that's true! Maybe it'd be easier if you looked at the direction of the motion line, which is a line perpendicular to the wavefronts. Hopefully, you will notice that the direction line of the wavefronts in medium B is closer to the normal than the line in the previous medium. I believe that all the wavefronts have prevented you from thinking about the direction lines. In addtion, direction lines are the ones taken into account when dealing with Snell's law. Edited September 15, 2012 by IB-Adam Reply Link to post Share on other sites More sharing options...
eelnedross Posted September 23, 2012 Report Share Posted September 23, 2012 (edited) Hey! This question seems to be easy, but the last one has been difficult for me to solve. How can i resolve it without any numbers for the resistance? Or use P = VI?Thank you! Edited September 23, 2012 by eelnedross Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted September 24, 2012 Report Share Posted September 24, 2012 Hey! This question seems to be easy, but the last one has been difficult for me to solve. How can i resolve it without any numbers for the resistance? Or use P = VI?Yes, the resistance of each bulb is 100/3 = 33.3 ohms.So the power output of bulb B is 36/33.3 = 1.08 W. Reply Link to post Share on other sites More sharing options...
IB-Adam Posted September 25, 2012 Report Share Posted September 25, 2012 But on 6(a), how could that be explained? Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted September 25, 2012 Report Share Posted September 25, 2012 But on 6(a), how could that be explained?The student's prediction in 6(a) is not correct. When the voltage is applied to the circuit by closing the switch, the free electrons everywhere in the circuit begin to drift towards the positive terminal of the battery and all three bulbs light. 1 Reply Link to post Share on other sites More sharing options...
MLI Posted September 25, 2012 Report Share Posted September 25, 2012 Does anybody know when there is a uniform field acting normally to the plane of paper, why do we consider the field as a magnetic field not an electric??? and how could we reference to the circular motion in order to justify the answer?? also can anybody explain this formula or at least its symbols r= (mv)/(Bq)Thanks 1 Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted September 25, 2012 Report Share Posted September 25, 2012 Does anybody know when there is a uniform field acting normally to the plane of paper, why do we consider the field as a magnetic field not an electric??? and how could we reference to the circular motion in order to justify the answer?? also can anybody explain this formula or at least its symbols r= (mv)/(Bq)ThanksI'm not sure that I have understood the question, but either a magnetic or an electric field could be set up normally to the plane of a sheet of paper. In the case of a uniform magnetic field a moving charged particle would describe a circular orbit, whereas in the case of an electric field the particle would be deflected towards or away from the paper.The formula r=(mv)/(Bq) would give the radius of the circular orbit that a charge q of mass m would follow when moving with speed v in a uniform magnetic field B. 1 Reply Link to post Share on other sites More sharing options...
IB Smacher Glau Posted September 29, 2012 Report Share Posted September 29, 2012 What's the SI unit for density ? shoudn't it be Kgm^-3 ? why the answer is JKg^-1 Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted September 29, 2012 Report Share Posted September 29, 2012 What's the SI unit for density ? shoudn't it be Kgm^-3 ?why the answer is JKg^-1Yes, density is of course measured in Kgmˆ-3.JKgˆ-1 is a unit of specific energy (of food, for example).To what question are you referring? Reply Link to post Share on other sites More sharing options...
IB Smacher Glau Posted September 30, 2012 Report Share Posted September 30, 2012 What's the SI unit for density ? shoudn't it be Kgm^-3 ?why the answer is JKg^-1Yes, density is of course measured in Kgmˆ-3.JKgˆ-1 is a unit of specific energy (of food, for example).To what question are you referring?it's in one of the past papers questions the answer is Jkg^-1 Reply Link to post Share on other sites More sharing options...
eelnedross Posted September 30, 2012 Report Share Posted September 30, 2012 To IB Smacher: It is the unit for energy density!On the other hand, does anyone know how to solve this question?Say, is there a strict relationship between the period and the displacement? Or just the frequency? Also, how can someone define a phase difference? What does it mean? A difference between periods? Furthermore, how to tackle this question? The only answer i can get is B (Unless my mathematics is failing me...)Thank you IBS!! 1 Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted October 1, 2012 Report Share Posted October 1, 2012 The phase difference between the waves is 2pi/4 = pi/2 rad. (Answer C)Furthermore, how to tackle this question? The only answer i can get is B (Unless my mathematics is failing me...)By the Stefan-Boltzmann law the correct answer is A, provided that either surfaces X and Y have the same area, or that "emit radiation at the same rate" refers to the rate at which energy is radiated per unit area. Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted October 1, 2012 Report Share Posted October 1, 2012 What's the SI unit for density ? shoudn't it be Kgm^-3 ?why the answer is JKg^-1Yes, density is of course measured in Kgmˆ-3.JKgˆ-1 is a unit of specific energy (of food, for example).To what question are you referring?it's in one of the past papers questions the answer is Jkg^-1What is the exact question to which Jkg^-1 is given as the answer? Reply Link to post Share on other sites More sharing options...
IB Smacher Glau Posted October 1, 2012 Report Share Posted October 1, 2012 (edited) the previous question is a mistake I guess from the QBM102.H1.28how can this be solved ? Edited October 1, 2012 by IB Smacher Glau Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted October 1, 2012 Report Share Posted October 1, 2012 The de Broglie wavelength of the electrons is inversely proportional to their momentum; their momentum is proportional to the square root of their kinetic energy; and their kinetic energy is proportional to the potential difference through which they are accelerated.Hence the de Broglie wavelength is inversely proportional to the square root of the potential difference. 1 Reply Link to post Share on other sites More sharing options...
IB Smacher Glau Posted October 1, 2012 Report Share Posted October 1, 2012 (edited) Thnxs .. Another questions are1) N10.H1.27I don't know how to get the answer .. explanation plz2) M092.H1.23Why the answer is B ? isn't be C ?3) M111.H1.20 "A sinusoidal ac power supply has rms voltage V and supplies rms current I. What is the maximum instantaneous power delivered?how it's 2VI ? Edited October 1, 2012 by IB Smacher Glau Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted October 1, 2012 Report Share Posted October 1, 2012 1) N10.H1.27I don't know how to get the answer .. explanation plzRMS voltage = 15/sqrt2So average power = ((15/sqrt2)ˆ2)/R = (45/2)W. (Answer A) 1 Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted October 1, 2012 Report Share Posted October 1, 2012 M092.H1.23Why the answer is B ? isn't be C ?The magnetic flux linking the disc is proportional to the cosine of the angle between the magnetic field direction and the normal to the plane of the disc, which is the complement of the angle theta. So the correct answer is B. 1 Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted October 1, 2012 Report Share Posted October 1, 2012 M111.H1.20 "A sinusoidal ac power supply has rms voltage V and supplies rms current I. What is the maximum instantaneous power delivered?how it's 2VI ?Peak voltage = (sqrt2)VPeak current = (sqrt2)ISo maximum instantaneous power = ((sqrt2)ˆ2)VI = 2VI. 1 Reply Link to post Share on other sites More sharing options...
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