This discussion is now closed.
Check out other Related discussions
- Confusing Capacitor question
- OCR A Physics 2018 paper 2 capacitors
- GCSE Exam Discussions 2024
- A level physics question Capacitance (2)
- A-level Exam Discussions 2024
- Capacitors
- A level physics capacitors
- Edexcel A Level Physics Paper 1: Advanced Physics I 9PH0 01 - 24 May 2023 [Exam Chat]
- need help please!
- Edexcel A Level Physics Paper 3: 9PH0 03 - 15th June 2023 [Exam Chat]
- Capacitor Question (PHYS)
- A level Physics Capacitance question (1)
- Engineering maths help
- IsaacPhysics Discharging a Capacitor help
- Physics OCR A-level PAG 9.2
- Capacitors
- Isaac physics A Square Pulse C3 - PLEASE help
- Edexcel GCSE Foundation tier Maths Paper 3 3F (1MA1) - 14th June 2023 [Exam Chat]
- AQA A Level Physics Paper 2 7408/2 - 10 Jun 2022 [Exam Chat]
- hypothesis Testing with only > Mean side of z table
Capacitor discharge rate question (from Edexcel PHY5 June 2002 paper)
Hurrah. I dislike the electrical parts of physics at the best of times. I really don't like capacitor stuff! I have found a question and I don't know what formulae to use to answer it - can anyone give me a nudge in the right direction?
*the scene is set* you have a defibrillator using a voltage of 6000V with a capacitance of 20 microF.
a) Find the charge on the plates when charged to 6000V
I used Q=VC and get 0.12C - I think I'm fine here.
b) Calculate the energy stored in the capacitor.
I used E=0.5xCxVsquared. Got 360J and think I'm ok here too..
then came
"When the capacitor is discharged there is an initial curren to 40A through the patient. Calculate the resistance of the body tissue between the electrodes."
Can I just assume the initial voltage is 6000V then use R=V/I? Doing that gave me 150ohms which sounds reasonable I suppose.
but then, it's the last part that really throws me. Assuming a constant discharge rate of 40A, calculate how long it would take to discharge the capacitor.
-I don't know what to do here. One of my textbooks suggests using 5 times the Time constant (CR) for the time at which the capacitor can be considered to be effectively discharged. But this wasn't what we were taught in college. Should I use this method or is there a better, nicer one I can use instead?
Many Thanks!!
*the scene is set* you have a defibrillator using a voltage of 6000V with a capacitance of 20 microF.
a) Find the charge on the plates when charged to 6000V
I used Q=VC and get 0.12C - I think I'm fine here.
b) Calculate the energy stored in the capacitor.
I used E=0.5xCxVsquared. Got 360J and think I'm ok here too..
then came
"When the capacitor is discharged there is an initial curren to 40A through the patient. Calculate the resistance of the body tissue between the electrodes."
Can I just assume the initial voltage is 6000V then use R=V/I? Doing that gave me 150ohms which sounds reasonable I suppose.
but then, it's the last part that really throws me. Assuming a constant discharge rate of 40A, calculate how long it would take to discharge the capacitor.
-I don't know what to do here. One of my textbooks suggests using 5 times the Time constant (CR) for the time at which the capacitor can be considered to be effectively discharged. But this wasn't what we were taught in college. Should I use this method or is there a better, nicer one I can use instead?
Many Thanks!!
You have worked out the charge stored. You have the current (assumed constant)
Just use Q = I x t to get t.
Just use Q = I x t to get t.
Where Did You Get This Paper From!? Is The Practical There?
How can we reasonably assume the discharge rate to be constant?
The charge in the capacitor is decaying exponentially so we differentiate and find that the current is also decaying exponentially.
The charge in the capacitor is decaying exponentially so we differentiate and find that the current is also decaying exponentially.
Related discussions
- Confusing Capacitor question
- OCR A Physics 2018 paper 2 capacitors
- GCSE Exam Discussions 2024
- A level physics question Capacitance (2)
- A-level Exam Discussions 2024
- Capacitors
- A level physics capacitors
- Edexcel A Level Physics Paper 1: Advanced Physics I 9PH0 01 - 24 May 2023 [Exam Chat]
- need help please!
- Edexcel A Level Physics Paper 3: 9PH0 03 - 15th June 2023 [Exam Chat]
- Capacitor Question (PHYS)
- A level Physics Capacitance question (1)
- Engineering maths help
- IsaacPhysics Discharging a Capacitor help
- Physics OCR A-level PAG 9.2
- Capacitors
- Isaac physics A Square Pulse C3 - PLEASE help
- Edexcel GCSE Foundation tier Maths Paper 3 3F (1MA1) - 14th June 2023 [Exam Chat]
- AQA A Level Physics Paper 2 7408/2 - 10 Jun 2022 [Exam Chat]
- hypothesis Testing with only > Mean side of z table
