15. (II) An electric field greater than about 3 × 10° V/m causes air to break down (electrons are removed from the atoms and then recombine, emitting light). See Section 17-2 and Table 17-3. If you shuffle along a carpet and then reach for a doorknob, a spark flies across a gap you estimate to be 1 mm between your finger and the doorknob. Estimate the voltage between your finger and the doorknob. Why is no harm done?

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**Electric Field and Sparks: A Detailed Analysis**

**Problem Statement:**

(II) An electric field greater than about \(3 \times 10^6\) V/m causes air to break down (electrons are removed from the atoms and then recombine, emitting light). Refer to Section 17-2 and Table 17-3. If you shuffle along a carpet and then reach for a doorknob, a spark flies across a gap you estimate to be 1 mm between your finger and the doorknob. Estimate the voltage between your finger and the doorknob. Why is no harm done?

**Solution:**

1. **Understanding the Breakdown of Air:**
   - When the electric field exceeds approximately \(3 \times 10^6\) V/m, the air ionizes, and electrons are liberated from atoms, resulting in a discharge of energy as light, creating a spark.

2. **Estimating the Electric Field Gap:**
   - Distance between finger and doorknob: \(d = 1 \text{ mm} = 0.001 \text{ m}\)
   - Electric field causing breakdown: \(E = 3 \times 10^6 \text{ V/m}\)

3. **Calculating the Voltage:**
   - Voltage (\(V\)) can be estimated using the relationship \(V = E \times d\)
   - Given values: 
     \[
     V = (3 \times 10^6 \text{ V/m}) \times (0.001 \text{ m}) = 3000 \text{ V}
     \]

4. **Conclusion - Why No Harm is Done:**
   - The spark is of very short duration and the amount of energy involved is relatively low.
   - Human skin acts as a good insulator.
   - The current involved in the spark is minimal and not enough to cause harm.

This analysis provides an estimation of the voltage that can arise in a common scenario and explains why a common static discharge, such as touching a doorknob after walking on a carpet, does not typically cause harm despite the high voltage involved.
Transcribed Image Text:**Electric Field and Sparks: A Detailed Analysis** **Problem Statement:** (II) An electric field greater than about \(3 \times 10^6\) V/m causes air to break down (electrons are removed from the atoms and then recombine, emitting light). Refer to Section 17-2 and Table 17-3. If you shuffle along a carpet and then reach for a doorknob, a spark flies across a gap you estimate to be 1 mm between your finger and the doorknob. Estimate the voltage between your finger and the doorknob. Why is no harm done? **Solution:** 1. **Understanding the Breakdown of Air:** - When the electric field exceeds approximately \(3 \times 10^6\) V/m, the air ionizes, and electrons are liberated from atoms, resulting in a discharge of energy as light, creating a spark. 2. **Estimating the Electric Field Gap:** - Distance between finger and doorknob: \(d = 1 \text{ mm} = 0.001 \text{ m}\) - Electric field causing breakdown: \(E = 3 \times 10^6 \text{ V/m}\) 3. **Calculating the Voltage:** - Voltage (\(V\)) can be estimated using the relationship \(V = E \times d\) - Given values: \[ V = (3 \times 10^6 \text{ V/m}) \times (0.001 \text{ m}) = 3000 \text{ V} \] 4. **Conclusion - Why No Harm is Done:** - The spark is of very short duration and the amount of energy involved is relatively low. - Human skin acts as a good insulator. - The current involved in the spark is minimal and not enough to cause harm. This analysis provides an estimation of the voltage that can arise in a common scenario and explains why a common static discharge, such as touching a doorknob after walking on a carpet, does not typically cause harm despite the high voltage involved.
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