jang
is not my real name
question 7
the current flowing in a DC motor reduces while the motor's speed incrases. How can this change in current be accounted for?
answer: b) the back emf reduces the resistance leading to a reduction in the dcurrent in the circuit
-edit- sorry wait the real answer is c) the increase in kinetic energy of the motor must be matched by a decrease in electrical energy in the circuit
(answer for (b) makes sense to me and i could choose b. but answer (c) talks bout conservation of energy -nonsense no? coz current is constantly being provided by an external circuit.. innit?
question 8
the question reads: what type of current would be produced by the motor? [there's a picture of a DC motor]
the choices are:
a) dc of constant magnitude
b) dc of varying magnitude
c) ac
d) none
... the answer is b.. which i dont get... it's a motor (they said motor atleast twice in q) :/ how does it make current? not that emf bs is it? (isnt emf only for ac?)
question 10
a coil is rotated in an area of constant magnetic flux density. which graph respresents the variatin of magnetic flux as the coil rotates?
all graphs in the answer have flux on the y axis and time on the x axis
a) [a flat graph (zero gradient) parallel to the x axis]
b) [sine graph]
c) [sine graph made of straight lines u get?]
d) [absolute value of sine graph]
if the magnetic flux density is constant, wouldnt the magnetic flux just remain constant?
the answer is b... WHY!
q17 (b)
theres a lot of numbers in this q. plz refer to it if u hav it -- for the initial calculation of the acceleration, wouldnt u hav to add 85kg (mass of man) to the mass of the rocket first as the thrust is acting on both the man and the rocket?
q18
observer A sits in te middle of a train travelling at ahigh speed past a railway station as shown in the the picture (i cant draw). Observer B stands on the station platform. Lightning strikes the front and back of the train at the moment observer A passes observer . Anaylse the statements of both observers regarding the order of lightning strikes (5 marks)
its about simultaneity, but inverted?? how would u answer this?
q23(b)analyse the competing technologies of edison and westinghouse for the supply of domestic electricity 5 marks
competing technologies? isnt the syll dot point: discuss the competition between these guys?
q25bthis question is just whack. we hav to find planck's constant from a graph with inacurrate data, and fullmarks are only allocated for deducing an accurate constant from the graph's slope
plz help solve these guysh!
the current flowing in a DC motor reduces while the motor's speed incrases. How can this change in current be accounted for?
answer: b) the back emf reduces the resistance leading to a reduction in the dcurrent in the circuit
-edit- sorry wait the real answer is c) the increase in kinetic energy of the motor must be matched by a decrease in electrical energy in the circuit
(answer for (b) makes sense to me and i could choose b. but answer (c) talks bout conservation of energy -nonsense no? coz current is constantly being provided by an external circuit.. innit?
question 8
the question reads: what type of current would be produced by the motor? [there's a picture of a DC motor]
the choices are:
a) dc of constant magnitude
b) dc of varying magnitude
c) ac
d) none
... the answer is b.. which i dont get... it's a motor (they said motor atleast twice in q) :/ how does it make current? not that emf bs is it? (isnt emf only for ac?)
question 10
a coil is rotated in an area of constant magnetic flux density. which graph respresents the variatin of magnetic flux as the coil rotates?
all graphs in the answer have flux on the y axis and time on the x axis
a) [a flat graph (zero gradient) parallel to the x axis]
b) [sine graph]
c) [sine graph made of straight lines u get?]
d) [absolute value of sine graph]
if the magnetic flux density is constant, wouldnt the magnetic flux just remain constant?
the answer is b... WHY!
q17 (b)
theres a lot of numbers in this q. plz refer to it if u hav it -- for the initial calculation of the acceleration, wouldnt u hav to add 85kg (mass of man) to the mass of the rocket first as the thrust is acting on both the man and the rocket?
q18
observer A sits in te middle of a train travelling at ahigh speed past a railway station as shown in the the picture (i cant draw). Observer B stands on the station platform. Lightning strikes the front and back of the train at the moment observer A passes observer . Anaylse the statements of both observers regarding the order of lightning strikes (5 marks)
its about simultaneity, but inverted?? how would u answer this?
q23(b)analyse the competing technologies of edison and westinghouse for the supply of domestic electricity 5 marks
competing technologies? isnt the syll dot point: discuss the competition between these guys?
q25bthis question is just whack. we hav to find planck's constant from a graph with inacurrate data, and fullmarks are only allocated for deducing an accurate constant from the graph's slope
plz help solve these guysh!
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