UPSC Prelims 2005 Q18: Science & Technology – Biology
What is the order of magnitude of electric resistance of the human body (dry)?
- (a) 10² ohm
- (b) 10⁴ ohm
- (c) 10⁶ ohm
- (d) 10⁸ ohm
Answer: (b) 10⁴ ohm
Explanation
Electrical resistance of the dry human body
| Condition | Approximate resistance |
|---|---|
| Dry skin | About 10^4 ohm order for body resistance |
| Wet skin | About 10^3 ohm or less |
| Internal body | About 300 to 500 ohm |
| Option (b) | 10^4 ohm matches the standard answer |
The standard answer for the order of magnitude of dry human body resistance is 10^4 ohm.
Answer: (b) 10^4 ohm.
Why each option is right or wrong
- (a) Incorrect. 10^2 ohm is closer to internal body resistance.
- (b) CORRECT. Dry body resistance is of the order 10^4 ohm.
- (c) Incorrect. 10^6 ohm is higher than the standard answer.
- (d) Incorrect. 10^8 ohm is far too high.
Key point
Dry body: about 10^4 to 10^5 ohm; wet skin: about 10^3 ohm; so wet hands raise shock risk.
Remember
Dry human body resistance is of the order 10^4 ohm.
Common mistakes
- Choosing a very low value for a dry body.
- Forgetting that moisture reduces skin resistance.
- Mixing body resistance with that of insulators.
Exam tip
Higher skin resistance when dry, lower when wet.
Sources
- NCERT Class XII Physics — Current Electricity
- International Electrotechnical Commission — IEC 60479-1: Effects of current on human beings and livestock