PumpkinBreath
- Feb 1, 2015
- 2
- Joined
- Feb 1, 2015
- Messages
- 2
Hello all
I am enrolled on a foundation program for electrical and electronic degree students. We have been set a simple test circuit to introduce us to the topic to test the internal resistance of a Function Generator (FG). I generated a DC Voltage of 0.0063V, coupled with an AC output Voltage of 1.003V at a frequency of 1.0048KHz.
Using this output we tested the Internal Resistance of the Function Generator (Ri), through Simulated Variable Resistor (R) in parallel with a Digital Multimeter, at varying resistance values (20-200 Ohms, collectively; R). A table was produced to show the different Resistance values (R) against the Voltage across the Simulated Variable Resistor (Vr).
The schematic and the graph are attached.
So, then we were told to draw a line on the graph at Vr = 0.5V and use a Line of Best Fit through our graph to find a value for Ri where the X-Y axis crossed. From this line we were asked to derive an equation for Vr based on the:
Supply Voltage (Vs)
Internal Resistance of FG (Ri)
Varied Resistance (R)
I calculated that since;
Vs = I(R+Ri) then,
Vs = IRi + Vr thus
Vr = Vs - IRi
This makes sense seeing that:
Vs = 1V
Vr = 0.5V
Ri = 65 Ohms
I = 0.0077A therefore;
1 - (7.7^10-3 x 65) = 0.5V
I'm happy so far. So then they ask what is Vr when R = Ri?
My query is that I don't understand this question.
Surely when the value of R = Ri, then Vr will still = Vs - IRi because to calculate the Voltage across the Varied Resistor we still have work out the Supply Voltage (Vs) minus the sum of the Two Resistances multiplied by the Current (I)?
Am I misreading the question perhaps?
Any advice/guidance on this would be greatly appreciated because I am stumped as to whether they are looking for another formula or if I'm correct in my idea that nothing should change.
Thanks very much!!
I am enrolled on a foundation program for electrical and electronic degree students. We have been set a simple test circuit to introduce us to the topic to test the internal resistance of a Function Generator (FG). I generated a DC Voltage of 0.0063V, coupled with an AC output Voltage of 1.003V at a frequency of 1.0048KHz.
Using this output we tested the Internal Resistance of the Function Generator (Ri), through Simulated Variable Resistor (R) in parallel with a Digital Multimeter, at varying resistance values (20-200 Ohms, collectively; R). A table was produced to show the different Resistance values (R) against the Voltage across the Simulated Variable Resistor (Vr).
The schematic and the graph are attached.
So, then we were told to draw a line on the graph at Vr = 0.5V and use a Line of Best Fit through our graph to find a value for Ri where the X-Y axis crossed. From this line we were asked to derive an equation for Vr based on the:
Supply Voltage (Vs)
Internal Resistance of FG (Ri)
Varied Resistance (R)
I calculated that since;
Vs = I(R+Ri) then,
Vs = IRi + Vr thus
Vr = Vs - IRi
This makes sense seeing that:
Vs = 1V
Vr = 0.5V
Ri = 65 Ohms
I = 0.0077A therefore;
1 - (7.7^10-3 x 65) = 0.5V
I'm happy so far. So then they ask what is Vr when R = Ri?
My query is that I don't understand this question.
Surely when the value of R = Ri, then Vr will still = Vs - IRi because to calculate the Voltage across the Varied Resistor we still have work out the Supply Voltage (Vs) minus the sum of the Two Resistances multiplied by the Current (I)?
Am I misreading the question perhaps?
Any advice/guidance on this would be greatly appreciated because I am stumped as to whether they are looking for another formula or if I'm correct in my idea that nothing should change.
Thanks very much!!