UPSC Prelims 2010 Q13: Science & Technology – Computer & Information Technology
Consider the following :
1. Bluetooth device
2. Cordless phone
3. Microwave oven
4. Wi - Fi device
Which of the above can operate between 2.4 and 2.5 GHz range of radio - frequency band ?
- (a) 1 and 2 only
- (b) 3 and 4 only
- (c) 1, 2 and 4 only
- (d) 1, 2, 3 and 4
Answer: (d) 1, 2, 3 and 4
Explanation
Which devices use the 2.4-2.5 GHz radio band
This frequency band is a commonly used, unlicensed ISM (Industrial, Scientific, Medical) band.
| Device | Verdict | Reason |
|---|---|---|
| 1. Bluetooth device | Correct | Bluetooth operates within the 2.4 GHz ISM band |
| 2. Cordless phone | Correct | Many cordless phones also operate in the 2.4 GHz band |
| 3. Microwave oven | Correct | Microwave ovens use roughly 2.45 GHz to excite water molecules, within this same band |
| 4. Wi-Fi device | Correct | Wi-Fi (802.11b/g/n) commonly operates in the 2.4 GHz band |
The 2.4 GHz ISM band's crowded users:
| Point | Detail |
|---|---|
| Band type | Unlicensed ISM band |
| Users | Bluetooth, cordless phones, microwave ovens, Wi-Fi |
| Consequence | Frequent interference between these devices |
Answer: (d) 1, 2, 3 and 4.
Why each option is right or wrong
- (a) Incorrect. Devices 3 and 4 (microwave ovens, Wi-Fi) also operate in this band, so '1 and 2 only' is too narrow.
- (b) Incorrect. Devices 1 and 2 (Bluetooth, cordless phones) also operate in this band, so '3 and 4 only' is incomplete.
- (c) Incorrect. Device 4 (Wi-Fi) is also in this band, so '1, 2 and 4 only' wrongly excludes microwave ovens.
- (d) CORRECT. All four devices — Bluetooth, cordless phones, microwave ovens, and Wi-Fi — operate in the 2.4-2.5 GHz ISM band.
Key point
The 2.4-2.5 GHz unlicensed ISM band is shared by Bluetooth, cordless phones, microwave ovens, AND Wi-Fi devices — all four, which is why they can interfere with each other.
Remember
2.4-2.5 GHz band users: Bluetooth, cordless phones, microwave ovens, and Wi-Fi — all four.
Common mistakes
- Assuming microwave ovens are unrelated to radio-frequency communication devices.
- Missing that cordless phones, an older technology, also share this crowded band.
- Underestimating how many common household devices compete for the same unlicensed spectrum.
Exam tip
2.4 GHz ISM band is crowded: Bluetooth + Wi-Fi + cordless phones + microwave ovens all share it, causing real-world interference.
Sources
- International Telecommunication Union — Radio Regulations, Article 5 (industrial, scientific and medical band 2400–2500 MHz)
- Institute of Electrical and Electronics Engineers — IEEE 802.11: Standard for Wireless LAN