# Homework Help: Capacitance -Problem-

1. Jun 20, 2009

### Apprentice123

As a person moves in an environment dry, electric charge accumulates in the body. Since the body is in high voltage, positive or negative, can download by visible sparks or shocks. Consider a human body and separate the soil, with typical capacitance of 150pF.

(a) Load that the body produces a potential of 10,0kV ?

(b) Sensitive electronic equipment can be destroyed by electrostatic discharge of a person. A device can be destroyed by a discharge that releases an energy of 250x10^{-6}J. This corresponds to the voltage on the body ?

2. Jun 20, 2009

### negitron

Sounds like homework to me. How would YOU go about solving these problems?

3. Jun 21, 2009

### Apprentice123

I do not understand the problem. What should I calculate?

4. Jun 21, 2009

### Redbelly98

Staff Emeritus
(a) I am just guessing, but I think "load" means charge. So calculate the charge.

5. Jun 21, 2009

### Apprentice123

Yes. I also think it load is charge

6. Jun 21, 2009

### Redbelly98

Staff Emeritus
Have you reviewed the equations that involve capacitance? That is where to start.

7. Jun 21, 2009

### negitron

Specifically, you want to find the equation which relates capacitance, charge and voltage. And the equation which relates charge, voltage and energy.

8. Jun 23, 2009

### Apprentice123

I think:

a) Q = C.V

Q = (150x10^{-12})x(10x10^{3})
Q = 1.5x10^{-6} coulomb

Alternative (b) I do not understand

9. Jun 23, 2009

### Staff: Mentor

Correct equation and calculation for (a).

Now, for (b), you need an equation that relates capacitance, voltage and the energy stored on that capacitance...

10. Jun 25, 2009

### Apprentice123

I find
(b) U = 1/2 * C * V^2
V = 1825,74 V

11. Jun 25, 2009

### Redbelly98

Staff Emeritus
Looks good! Though we really only know that number to 2 significant figures.