A video – bearing a watermark pointing to an Instagram handle called @fenoogreek – has been doing the rounds on WhatsApp. In the video, a young man claims to feel a minor electric shock when he puts his hand on the shoulders of a young woman seated on a couch and working on a laptop that is charging. Both individuals exclaim, and the young man claims to know what is happening.
He fetches a handheld device and asks the woman to bring her hand close to it, and when she does, the device seems to produce some reading that the man claims is proof that there is a measurable electric current on her skin. The video concludes with the young man claiming that when such “dirty radiation” flows and accumulates in our bodies, it causes cancer.
The clip does not refer to electrical injuries that could result from contact with faulty appliances or power lines.
You might sometimes feel a small, tingling sensation when you touch a laptop with a metal casing if it is also charging. This is the result of a residual current flowing through the laptop’s body into a body of negative electric potential – usually called the ‘ground’. But these currents are very weak and not hazardous for humans.
The connection between your laptop’s charger and its power source should be such that current flows from the source into the laptop, through all the circuits, and back into the source, forming a closed loop. Current flows in the opposite direction of electrons. In this case, then, electrons flow from negative potential to positive potential – while the current flows the other way, from positive potential to negative. The laptop is just in the way.
A small fraction of current may escape the closed loop and linger on the laptop’s surface, especially if the surface is made of metal (a common example is Apple laptops). This current then flows to the ground through the body of the person touching the metal surface of the laptop. This is called a touch current.
You can prevent such touch currents by ensuring that your power source is properly grounded, including by using a three-pin plug instead of one with two pins.
Measuring the current
In the WhatsApp video, the young man appears to measure the strength of the electric field using a portable device. This device is an electromagnetic field (EMF) metre. Technical experts use EMF metres to detect and measure the quantum of electromagnetic radiation at a given spot.
This measurement will vary depending on the metre’s proximity to the source – in this case, the laptop. So it is not clear how placing one hand near the EMF metre while touching the laptop with the other, as the woman does in the video, alters the reading.
In fact, the device manual for the TriField TF2 EMF metre – also used in the video – states that the reading would be lower near a human body than farther away from it. This is because the human body shields electrical fields.
Finally, touch currents are too weak to influence the reading on an EMF metre. In the video, the woman speaks the metre reading out loud: “0, 1, 2… very little”, followed by “300”. She doesn’t specify the units, however.
Ionising v. non-ionising radiation
When a body emits radiation, it can do so in a range of frequencies depending on the emission conditions. This range of frequencies is what we know as the electromagnetic spectrum.
Electromagnetic waves include radio transmissions, visible light, X-rays and gamma rays. Higher frequency radiation like X-rays and gamma rays are classified as ionising radiation. The relatively high energy that each of their waves carry can knock electrons out of atoms. When this happens, the atom becomes an ion, and can trigger a cascade of changes within the body.
This is why exposure to significant doses of gamma rays can lead to DNA damage and potentially cause cancer (or, in a Marvel film, turn you into the Hulk). This is also why exposure to ionising radiation is strictly regulated – in India, by the Atomic Energy Regulatory Board.
Radiation whose waves carry energy that is not sufficient to ionise atoms is simply called non-ionising radiation. All electric transmission lines, electrical wiring and appliances emit electromagnetic waves. In India, they do so at a frequency of 50 Hz – known as the utility frequency. This is considered to be an ‘extremely low frequency’ (ELF) on the electromagnetic spectrum.
Such waves are incapable of ionising atoms within the body. In fact, their waves have less energy than visible light.
Does ELF radiation cause cancer?
There is no known mechanism by which non-ionising radiation can present a cancer risk.
Many studies have examined the possibility of a link between exposure to ELF radiation and cancer. They have reported no evidence for the claim that exposure to ELF radiation can cause cancer among adult humans.
There is tenuous evidence linking ELF magnetic field (not electric field) exposure to childhood leukaemia – but many scientists have refuted these claims as well. A WHO Task Group reached the same conclusion, that there is no link, 17 years ago.
Electricity and electric and electronic appliances have become ubiquitous in modern life. Electric appliances like TVs, refrigerators, air-conditioners, etc. emit only ELF radiation – as do charging (or discharging) laptops and smartphones. As a result, a certain level of exposure to ELF radiation has become inevitable. But there is no reason to suspect that this will cause cancer. As indicated earlier, visible light carries more energy than ELF radiation per wave.
In sum, there is no evidence in the scientific literature to justify the alarming claim that the WhatsApp video makes – that using a laptop while it is charging will cause cancer in the body.
Swetha P. is a science communicator and an aspiring physicist.