Category Archives: Uncategorized

Light Emitting Diodes (LEDs)

Notice anything different about bike lights recently? Just walking back from somewhere at night when you see a car coming towards you with beaming headlights approaching as cross the road. As this vehicle comes closer, you see that it’s not a car but actually a harmless cyclist. You’re confused on how a light small could produce such brightness.

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Well, due to a improvement in modern technology LED lights have become more efficient. These light emitting diodes which usually power bike lights now produce a lot more light energy instead of heat energy so the bulbs are much brighter as a result.

So, how does a LED emit light? Let’s start from the beginning, the usual filament lamp, also know as a an incandescent light, becomes bright when the piece of wire becomes hot due to electricity flowing through it.

Without any filament inside it, how does an LED light work? Well, it’s because of the movement of electrons in a semiconductor inside the light. Light can be emitted in a wave or particle form and in this case the light is emitted as a particle. With pin the LED there are many atoms and the electrons are constantly moving between the electron shells, this gives off energy. So, this energy produced is in the form of a photon, a particle of light. For the light to be visible, the diode must be made out of a material, for example a silicon diode is made so the electrons only travel short distances meaning that the photons have a low frequency making the light emitted visible to the eye.

In the house, however, it’s a bit of a different story. LEDs only work off direct current and the houses electricity is alternating current so to gets the bulbs to work the ac must be converted to dc. This means that LED bulbs are less efficient in the household because of the energy that is used to transform the current. This shows that although LEDs are extremely useful in some ways, on a bigger scale they do become less efficient.

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Why does ice float?

Our atmosphere contains a number of gases, with a variety of relative atomic masses, including nitrogen (14), carbon dioxide (22), oxygen (16) and argon (18). Our atmosphere’s temperature can range from 50 degrees Celsius to -50 degrees Celsius depending on which layer you’re in.

Although water (9) has a considerably lower relative atomic mass than the Earth’s atmospheric gases, it is still a liquid at room temperature. You’d think that because of its low relative atomic mass, it would be harder for the molecules to bond at low temperatures. But water has to be heated up to 100 decrees Celsius to boil and freezes at 0 degrees Celsius, whereas the atmospheric gases are all gases at minus temperatures (although they have a higher relative atomic mass), which is uncharacteristic of molecules that size at those temperatures.

Impossible you say?

It’s all due to hydrogen bonding between the molecules. The oxygen molecules pull the electrons away from the hydrogen because it’s lack of electrons. Oxygen has 16 electrons meaning that it’s final electron shell is not full (having 6 electrons instead of 8) making it unhappy. To gain 18 electrons, the oxygen atom needs another 2, luckily the two hydrogen atoms both have one electron each, totalling up to the 18 electrons. The hydrogen also needs those electrons so the atoms are constantly fighting over them causing the hydrogen protons to be exposed which allows hydrogen bonding and is the reason for waters unusual boiling and freezing points.

ImageWhen water freezes, it causes a crystalline structure because of hydrogen bonding leading to a solid with a lower density than liquid water. This is why ice floats in a liquid, because it has a lower density.

How Could the Northern Lights Bring Our Demise?

Tara Magill

Last week, I had the opportunity to visit UCL and attend a lecture entitled ‘Solar Eruptions, Earth’s Magnetic Field & Why Space Weather is Important to Modern Society’. At first glance, this may seem like an exceedingly tedious subject, but over the course of 90 minutes, Dr Anasuya Aruliah of the Atmospheric Physics Laboratory at UCL Department of Physics & Astronomy explained to the packed lecture hall how the activity of the sun has such a massive impact in all of our lives.

We all know what a huge role the sun has played in the history of the solar system – without it, there would be no solar system, let alone life as we know it. For thousands of years, our celestial parent was worshiped as a deity by countless cultures – and rightly so. Before the development of science, it would be easy to believe that this ball of hot plasma was our God, bringing life to this otherwise desolate planet and providing us with the warmth and light necessary to keep living.

The sun continues to provide us with all of our energy, whether it be from the obvious solar panels or from the fossil fuels that we burn (the sun provided the conditions necessary for life, and so produced the animals and plants that are now fossils beneath our surface). However, there are many, less apparent ways that the sun has major effects on our daily business here on planet Earth.

Fig. 1: The tubes represent magnetic field lines, blue when the field points towards the centre and yellow when away. The rotation axis of the Earth is centred and vertical. The dense clusters of lines are within the Earth’s core.

As you can tell from the title, Dr Aruliah’s presentation was surrounding the effects that the magnetic fields of both Earth and the Sun interact and how this can change our lives. This field of physics is becoming more and more prominent; this is due to an impending switch in the direction of the Earth’s magnetic field, which could leave us vulnerable to powerful solar winds capable ofknocking out global communications and power.

The Earth is constantly bombarded with solar winds from the sun. However, the only time that this is visible is during the aurora, also known as the Northern Lights. This phenomenon occurs when the solar wind is strong enough to interact with our atmosphere. Other planets with a much thinner atmosphere, such as Mercury, do not experience this phenomenon.

Fig. 2: The heliospheric current sheet results from the influence of the Sun’s rotating magnetic field on the plasma in the interplanetary medium (solar wind). The wavy spiral shape has been likened to a ballerina’s skirt.

As seen in Figure 2, the solar winds are often deflected from our planet by our magnetic field, resulting in the plasma being sent off to other parts of the solar system.This protects us from the harmful effects of the radiation they emit. However, if our magnetic field were to weaken or reverse, we would be far more vulnerable.

Our communications systems could be completely wiped out for days, months or potentially years, and technology would be severely affected. Transmission equipment would be ineffective, plunging us back into the dark ages.

While this seems extremely unlikely, it is still very possible, and so scientists are investing increasing amounts of time on improving our security and creating equipment to help us withstand this powerful radiation.

All we can hope is that our magnetic field protects us long enough so that we can develop this security, or we could face technological development regressing over 1000 years.

Olympic Science – The track

BBC News made an interesting post about the science of the Olympic running track.  The track has to be designed to be comfortable for the athletes to run on as well as giving them the best conditions for top speeds.  To achieve this it has been made of two layers.  The top layer is designed to maximise the friction between the show and the track, a feature which can be enhanced by spikes added to the shoes.  Most people associate friction with being slowed rather than speeding up but without friction we wouldn’t be able to move at all.  As the athlete runs, the ball of their foot pushes backwards onto the track.  As a result of Newton’s 3rd Law of Motion this causes the track to push forward on the athlete with equal force.  The more friction there is between the shoe and the track, the more energy can be transferred into this forward push, rather than the foot slipping backwards.

The lower surface is designed for shock absorption.  This not only provides an extra ‘spring’ to the athlete, pushing them forwards, but also helps reduce damage to their joints.  When the surface that you are running on is hard, such as concrete, as you hit your feet against the floor with each step there is a high rate of change in momentum which leads to a large force being applied to the joints.  By using a ‘springy’ surface the time taken for each impact with the floor is increased, thus reducing the rate of change of momentum and hence the force applied to the joints.