physics help !!

[halosh92]

its D
because when u pass current through the iron core a magnetic field is induced at one end.a magnetic field is also induced at the other end..causing a voltage and thus higher or lower currnet *depends on the tansformer whether its a step down or step up transformer*
hope it helped 

[astarmathsandphysics]

Thanks astar....

but why is 35 D ?

need an answer please...

The motor stops because the voltage across it is zero.

[esso]

yah understood .... Thanks everyone for the help 

[nid404]

but astar how is the pd decreasing, cuz the current is increasing( resistance is reduced.) And when the current increases rotation in a motor is faster no?? Plz explain astar...i too am giving my exam tomorrow

[QuickSilver]

Voltage Decreases because voltage is the pressure basically, so if there is less resistance then this means that ekectrons will produce a less effort to pass through decreasing the pressure, and since Voltage is INVERSLY proportional to current, then when voltage decreases this casuses the current to increase causing the motor to spin faster


Right Sir??


Thanks

[nid404]

Voltage Decreases because voltage is the pressure basically, so if there is less resistance then this means that ekectrons will produce a less effort to pass through decreasing the pressure, and since Voltage is INVERSLY proportional to current, then when voltage decreases this casuses the current to increase causing the motor to spin faster


Right Sir??


Thanks

that is what i thought but the mark scheme says the motor stops...

[astarmathsandphysics]

but astar how is the pd decreasing, cuz the current is increasing( resistance is reduced.) And when the current increases rotation in a motor is faster no?? Plz explain astar...i too am giving my exam tomorrow

The voltage a cross the motor is the voltage across that part of the resistor between X and th other wire connecting the motor to the circuit. If you move the conact at x to the bottom of the resistor this voltage will be zero and the current and voltage and resistance in the circuit is irrelevant. Hence the motor stops

[QuickSilver]

but astar how is the pd decreasing, cuz the current is increasing( resistance is reduced.) And when the current increases rotation in a motor is faster no?? Plz explain astar...i too am giving my exam tomorrow

The voltage a cross the motor is the voltage across that part of the resistor between X and th other wire connecting the motor to the circuit. If you move the conact at x to the bottom of the resistor this voltage will be zero and the current and voltage and resistance in the circuit is irrelevant. Hence the motor stops

ohh so ok V and I are inversely proporional but when V=0 (zero), then no current can occur right??

[Kim]

their is this question in may 2007 no 3 cud sum 1 explain the answer to me?

[nid404]

but astar how is the pd decreasing, cuz the current is increasing( resistance is reduced.) And when the current increases rotation in a motor is faster no?? Plz explain astar...i too am giving my exam tomorrow

The voltage a cross the motor is the voltage across that part of the resistor between X and th other wire connecting the motor to the circuit. If you move the conact at x to the bottom of the resistor this voltage will be zero and the current and voltage and resistance in the circuit is irrelevant. Hence the motor stops

ok so when V is 0, rest pf the things are not to be considered..so now i understand that the resistor is acting like a potential divider.
thanks sir

[QuickSilver]

but astar how is the pd decreasing, cuz the current is increasing( resistance is reduced.) And when the current increases rotation in a motor is faster no?? Plz explain astar...i too am giving my exam tomorrow

The voltage a cross the motor is the voltage across that part of the resistor between X and th other wire connecting the motor to the circuit. If you move the conact at x to the bottom of the resistor this voltage will be zero and the current and voltage and resistance in the circuit is irrelevant. Hence the motor stops

yeah thanks sir, i understand too
ok so when V is 0, rest pf the things are not to be considered..so now i understand that the resistor is acting like a potential divider.
thanks sir

[astarmathsandphysics]

but astar how is the pd decreasing, cuz the current is increasing( resistance is reduced.) And when the current increases rotation in a motor is faster no?? Plz explain astar...i too am giving my exam tomorrow

The voltage a cross the motor is the voltage across that part of the resistor between X and th other wire connecting the motor to the circuit. If you move the conact at x to the bottom of the resistor this voltage will be zero and the current and voltage and resistance in the circuit is irrelevant. Hence the motor stops

ohh so ok V and I are inversely proporional but when V=0 (zero), then no current can occur right??

No V_motor=(V_supply*R_out/(R_out+R) where R is the other resistance in the cicuit

[astarmathsandphysics]

Yes it is a potential divider

[Kim]

hey Astar cud u help with  nov 2006 p1 q3?plz it will be really appreciated

[nid404]

hey Astar cud u help with  nov 2006 p1 q3?plz it will be really appreciated

60km/h

30km in 1/2 hour..so in 1 hour it will be 60

ans is D