# Help (Electrostatic/electric shock)

• Josh123
In summary, the problem involves determining the charge on a child's fingertip and the resistance of dry air between a metal truck and the fingertip. The breakdown field strength and the distance between the fingertip and the toy are given, and the energy needed to produce a burn is also a relevant factor. The solution would involve calculating the voltage that produces a spark, and then equating the energy of the charge with the energy needed for the burn.
Josh123
here's a problem that I am currently working on. I know the theory, but I'm not quite sure how to start this particular problem:

"Thomas was crawling around on the rug. When he reached for a metal truck, a prominent spark lasting 5mmsec appeared between his fingertip and the object. His fingertip was about 2 mm from his toy. His finger burnt (the area of the burned region was of 10^-4 m^2)

On that day, the air was cold and dry causing it to become conducting when the electric field reached 3*10^6 N/C."

My question is, how you I determine the charge on the child's fingertip?
How do I estimate the resistance of the dry air between the toy
truck and the child's fingertip? (I just would like to know how to start this problem.. you don't have to do the entire thing)

First you determine the voltage that gives a 2 mm spark (the breakdown field strength is given, but in other units than V/m).

Then you equate the energy when a charge Q goes through the calculated potential difference with the energy needed to produce such a burn (I do not know how to estimate that - are there more things given?).

To start this problem, we can use the formula for electric field:

E = V/d

Where E is the electric field, V is the potential difference, and d is the distance between the two objects. In this case, the potential difference can be calculated as the work done to move one unit of charge from one object to the other. We can estimate this value by using the formula:

V = W/Q

Where V is the potential difference, W is the work done, and Q is the charge on the child's fingertip.

To determine the charge on the child's fingertip, we can rearrange the equation to solve for Q:

Q = W/V

We can estimate the work done by the spark by using the formula for electrical energy:

W = QV

Since we know the potential difference (V) and the time (5mmsec) for which the spark lasted, we can estimate the work done.

Next, we can use the formula for resistance:

R = ρL/A

Where R is the resistance, ρ is the resistivity of the material (in this case, the dry air), L is the length of the air gap (2 mm in this case), and A is the cross-sectional area (10^-4 m^2 in this case).

To estimate the resistivity of dry air, we can use the formula:

ρ = 1/σ

Where ρ is the resistivity and σ is the conductivity of air. The conductivity of air can be determined using the formula:

σ = ne^2τ/m

Where n is the number of free electrons, e is the charge of an electron, τ is the relaxation time, and m is the mass of an electron. All of these values can be found in a table or can be estimated.

Once we have estimated the resistance of the dry air, we can use Ohm's law to calculate the current flowing through the air gap:

I = V/R

From there, we can use the formula for charge:

Q = It

Where Q is the charge, I is the current, and t is the time (5mmsec in this case).

I hope this helps you get started on the problem. Remember to always use the appropriate formulas and units, and to estimate values if necessary. Good luck!

## 1) What causes electrostatic shock?

Electrostatic shock is caused by the build-up of static electricity on the surface of an object. This can occur when two objects with different electrical charges come into contact or when an object with a high electrical charge comes into contact with a conductor, such as a person.

## 2) How can I prevent electrostatic shock?

To prevent electrostatic shock, you can take several precautions, such as wearing anti-static wristbands or using anti-static mats. You can also reduce static electricity by keeping the relative humidity in your environment above 40%, as dry air allows for easier build-up of static charge. Additionally, avoid wearing clothing made of synthetic materials, which are more likely to generate static electricity.

## 3) Is electrostatic shock dangerous?

In most cases, electrostatic shock is not dangerous. However, it can be uncomfortable and startling. In rare cases, a strong enough shock can cause muscle spasms or temporary loss of consciousness. People with medical devices such as pacemakers should take extra precautions to avoid electrostatic shock as it can interfere with the functioning of these devices.

## 4) Can electrostatic shock damage electronic devices?

Yes, electrostatic shock can damage electronic devices. The high voltage of the shock can disrupt the delicate electronic components and cause them to malfunction. To prevent this, it is important to discharge any static build-up before handling electronic devices and to use anti-static measures when working with them.

## 5) Can I get electrostatic shock from electronic devices?

Yes, it is possible to get electrostatic shock from electronic devices. This can happen when the device is not properly grounded or if you touch a component with a high electrical charge. To avoid this, make sure to handle electronic devices with care and discharge any built-up static electricity before touching them.

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