Different Stages of Lightning and its effect on Computers and Mobile Phones

Shelly Rajput

Department of Applied Sciences, Delhi Global Institute of Technology, Haryana, India.

*Corresponding Author E-mail: shelly.rajput@rediffmail.com

ABSTRACT:

It is common notion that electric gadgets like; computer, laptop and mobile phone could be a potential device for conducting lightning. It is also believed the electricity travelling through the radio waves associated with the devices and deliver a shock to the person using them. The present article is a review of different stages of cloud-to-ground lightning discharge and also explore the possibility of a computer, laptop and mobile phone providing a lightning path through the user to the ground.

KEYWORDS: Lightning, electric gadgets.

INTRODUCTION:

DIFFERENT STAGES IN A LIGHTNING DISCHARGE

A negative cloud-to-ground discharge, the most common earth flash, starts in cloud and brings tens of coulombs of negative cloud charge to the earth. The total discharge called FLASH has time duration of about half a second. It comprises of various discharge components, including three or four high current pulses called STROKES. Each stroke takes about a millisecond and the gap between strokes is of several tens of milliseconds.

The electric field change prior to the first return stroke in a negative cloud- to ground lightning has duration from a few milliseconds to a few hundred milliseconds. The stepped leader duration is typically 10 to 30ms. It follows that some of the observed pre first stroke field change and luminosity is due to a ‘Preliminary Breakdown’ within the cloud. Malan (1952,1955) gives the photographic evidence for the discharge occurring in the cloud and preceding the stepped leader. Beasley et al. (1982) have published statistical data on duration of electric field changes prior to stepped leader. The end of preliminary breakdown or beginning of stepped leader is often characterized by a train of relatively large bipolar pulses from VLF to VHF. Weidman et al. (1981) give the frequency spectrum and Beasley et al. (1982) confirm their locations.

After the breakdown the main discharge begins and the negative charge moves towards the ground in steps. This first stroke (first part of the flash) is called stepped leader. The step lengths are between 10 and 200m, with a pause time from 37 to 124µs as reported by Schonland (1956). Longer pause times are generally followed by longer step lengths. Step lengths are shorter near the ground. A fully developed stepped leader lowers up to 10 or more coulombs negative charge towards ground in tens of milliseconds with average speed of about 2x10⁵ m/s the average leader current is 100-1000A. Pathak and Rajput (2005) explained mechanism of higher frequency radiation from stepped leader and also computed the radiation due to stepped leader in HF range during ground discharge by using positive corona streamer model proposed by Pathak (1994). First stepped leader pulse just before return stroke is generally largest, about 10% of the peak value of the following return stroke field. The electric field produced by the charge on the leader enhances when some conducting object such as mound of earth, a tree or a transmission tower comes in its path. This field enhancement may cause upward electric discharge called leaders, connecting leaders, connecting discharges or streamers to emit from the object. The distance between the conduction object and tip of the downward moving leader when the connecting leader is just initiated is called “striking distance”. The two leaders then meet somewhere in between their positions, often halfway between. This is called ‘Attachment Process’.

When one of the upward moving discharge from the ground contacts the downward moving leader some tens of meters above the ground, the leader tip is connected to the ground potential. The leader channel is then discharged when a ground potential wave, the return stroke, propagates up the previously ionized leader path. Upward velocity of a return stroke is about one third the speed of light and the total transit time from ground to top of the channel is about 100µs. The first return stroke produces peak current of about 30KA near the ground, the time from zero to peak being a few microseconds. Currents measured at the ground fall to half of the peak value in about 50µs and current of the order of hundreds of amperes may flow for few milliseconds to several hundred milliseconds. The rapid release of return stroke energy heats the leader channel to a temperature near 30,000K and generates a high-pressure channel that expands and creates the shockwaves which become thunder. Pathak and Rajput (2021) computed the radiation due to return stroke in HF range during ground discharge by positive corona streamer model.

After the first set of stepped leader and return stroke, leader process again starts from the cloud. As the air column below is already partially ionized, the leader reaches the ground almost in a single or two steps. This is known as a dart leader. Thus the return strokes subsequent to the first in a flash to ground are usually initiated by dart leaders. Dart leader carry cloud potential earthward via an ionizing wave of potential gradient (Loeb,1966) and lower about 1C of negative charge in about 2ms. Thus they have a current of about 500A. Their velocities are between 1 to 23 x10⁶ m/s, shorter inter stroke intervals correspond to higher velocities.

ATTRACTION TO COMPUTERS:

Lightning carries huge amount of electricity and if that electricity makes it into electronic equipment it can do serious damage. The chance of a computer being struck by lightning are very high. Desktop PC must be disconnected from power, LAN and phone lines during a lightning. Even with good surge protectors it is still possible that computer may be damage. When the lightning hits a power line, it carries electric current of about 30KA, and that significantly exceeds the standard flow of electricity. Even an indirect hit, near a power line can send extra voltage and cause damage on computer.

The chances of laptops being struck by lightning are less likely. Laptops are safe to use during lightning if disconnected from power. Running laptop from battery is quite safe. The laptop connected to power point is at the same risk as a desktop computer during thunderstorms. The components of computers and laptops are likely to be in touch, are all plastic, so a shock is very unlikely. Wearing headphones could be at risk of either acoustic shock or electric shock as the headphones put electrical components close to head. It is advised to avoid headsets during thunderstorms and lightning.

Using Wi-fi, to access internet connection, Wi-fi modem or router is at risk because it is usually plugged both into a phone line and power point. The same electrical surge that affect computer can harm modem too.

ATTRACTION TO MOBILE PHONES:

There is a common belief that the mobile phones are risky when used outside during lightning and thunderstorm because lightning is attracted to metal. Agarwal (2013) in his course work explained that, the handsets generally contains insignificant amount of metal. Thus the chances of a mobile phone and cordless phones being struck by lightning is likely less. Mobile phones used indoor during lightning are perfectly safe because there is no wire through which electric discharge could travel. Also the belief that the lightning can follow the radio waves is complete unfounded.

CONCLUSION:

Lightning is an important natural phenomenon and plays significant role in earth’s ecosystem. On other hand there is destructive part of same fascinating phenomena. It is still unknown that why some places seem to be prone to lightning. Lightning strikes preferentially the tall structures like radio tower, buildings etc. A lightning strike causes death, injury to people and animals, damage and destruction to ground based structure, disturbs power and communication lines and also damages electrical equipment both inside and outside the building. Lightning can also harm the people using electronic devices by providing a less resistive path. A damage and fires are usually the result of lightning not being able to find a quick and easy path. Gadgets like computer, laptop and mobile phone are safe to be used during lightning and thunderstorm when they are unplugged. The parts of computer, laptop and mobile phone which are likely touched are made of plastic or they contain insignificant amount of metal so they are not risky when used unplugged.

REFERENCES:

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Received on 25.06.2021 Accepted on 19.07.2021

Research J. Engineering and Tech. 2021;12(3):90-92.

DOI: 10.52711/2321-581X.2021.00015