AS Physics Challenge help
Can anyone help me with these two questions from the AS Physics Challenge? Thanks
Original post by Cantthinkofnames
Can anyone help me with these two questions from the AS Physics Challenge? Thanks
How far have you progressed with these problems and where are you stuck?
Show us your workings and help us to help you.
Q1 have you drawn a free body diagram of the forces and tensions in the ropes?
Q2 the question tells you 5V is developed across the resistor parallel with the zener diode.
Using Kirchoff's voltage rule, what must the p.d. across the series resistor be?
Therefore what is the current flowing in the series resistor (ohms law)?
Using ohms law again, calculate the current in the parallel resistor.
You now have enough information to solve the problem by using Kirchoff's current rule for the branch currents.
Original post by uberteknik
Hello.
How far have you progressed with these problems and where are you stuck?
Show us your workings and help us to help you.
Q1 have you drawn a free body diagram of the forces and tensions in the ropes?
Q2 the question tells you 5V is developed across the resistor parallel with the zener diode.
Using Kirchoff's voltage rule, what must the p.d. across the series resistor be?
Therefore what is the current flowing in the series resistor (ohms law)?
Using ohms law again, calculate the current in the parallel resistor.
You now have enough information to solve the problem by using Kirchoff's current rule for the branch currents.
How far have you progressed with these problems and where are you stuck?
Show us your workings and help us to help you.
Q1 have you drawn a free body diagram of the forces and tensions in the ropes?
Q2 the question tells you 5V is developed across the resistor parallel with the zener diode.
Using Kirchoff's voltage rule, what must the p.d. across the series resistor be?
Therefore what is the current flowing in the series resistor (ohms law)?
Using ohms law again, calculate the current in the parallel resistor.
You now have enough information to solve the problem by using Kirchoff's current rule for the branch currents.
For Q2, how can you find the voltage across the series resistor without getting the voltage across the parallel resistors using Z?
For Q1, I've got the driving forces of both cars and the three tension forces, is there anything I've missed?
Original post by Cantthinkofnames
For Q2, how can you find the voltage across the series resistor without getting the voltage across the parallel resistors using Z?
The question tells you the zener holds the p.d. across the parallel resistor at 5V which, according to KVL, means 10 - 5 = 5V is dropped across the series resistor.
Original post by uberteknik
The question tells you the zener holds the p.d. across the parallel resistor at 5V which, according to KVL, means 10 - 5 = 5V is dropped across the series resistor.
Doesn't it mean that 5V is the voltage across the 400 ohm resistor alone, and not both of the resistors?
Original post by Cantthinkofnames
Doesn't it mean that 5V is the voltage across the 400 ohm resistor alone, and not both of the resistors?
Where has the other 5V gone?
The question says: "Z is a device which has the property of maintaining a potential of 5V across the 400 ohm resistor".
The supply voltage is 10V, therefore from Kirchoff's voltage rule (sum of the voltage drops around a circuit equals the supply voltage):
substituting values
The thing to realise is that the diode will hold 5V across the 400 ohms resistor whatever the supply voltage is. Which means the difference between the supply emf and the Zener diode voltage must be dropped across the series resistor.
There is now enough information to calculate the current flowing in the series resistor.
and also the current in the R400 ohm resistor path:
and from Krichoff's current rule for branch nodes
(edited 9 years ago)
I think the answer is
a) a1+a2 /2
b) 7.5mA
Correct me if im wrong
Posted from TSR Mobile
a) a1+a2 /2
b) 7.5mA
Correct me if im wrong
Posted from TSR Mobile
Original post by fading_away97
Actually I just think its a1+a2. Because its only horizontal forces shouldn't both sides then equal.
Posted from TSR Mobile
Posted from TSR Mobile
Original post by fading_away97
Actually I just think its a1+a2. Because its only horizontal forces shouldn't both sides then equal.
Posted from TSR Mobile
Posted from TSR Mobile
I think you were right first time. I hate modified Atwood machines though.
This, however, ought to be a simple case of working out what form the answer needs to have.
There are two cases you can consider 1) That your equation should be symmetric in that you can rename a1 a2 and vice versa (this rules out two out of four options)
and 2) what happens when both are equal
This eliminates any need to actually solve the problem as there's only one option that doesn't cause very weird things to happen
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