The picture shows a line of length a and another line of length b that are joined to make a line of length a + b. Note that a is longer than b. Now if a/b = (a + b)/a the result is called the golden ratio, φ. It has other names: for example, the… Continue reading 20.31 The golden ratio

Before you read this, I suggest you read post 20.27. The picture above shows a molecule of tartaric acid. This molecule is chiral – it is not identical to its mirror image (post 20.27). The form of tartaric acid shown in the picture is called D tartaric acid; its mirror image is called L tartaric… Continue reading 20.30 Diastereoisomers

Introductions Before you read this, I suggest you read posts 20.27 and 20.28. In post 20.27, we saw that optical isomerism occurs when a molecule is not identical to its mirror image. The two forms of the molecule are called optical isomers. They exist as the D or the L form that are mirror images… Continue reading 20.29 Properties of optical isomers

Before you read this, I suggest you read post 19.9. In post 19.9, we saw that light can be considered as an electromagnetic wave. This wave consists of an electric field and a magnetic field that oscillate perpendicular to the direction of propagation of the wave, as shown in the picture above. The electric field… Continue reading 20.28 Polarised light

Have you ever tried to put your right shoe on your left foot? Or your left shoe on your right foot? If you can do either, the result will be very uncomfortable! But the width, length and height of both shoes are identical. And the outer, inner and upper curvatures are all the same. So… Continue reading 20.27 Chirality

Before you read this, I suggest you read post 20.25 Normally, we think that objects spontaneously minimise their potential energy so that, for example, an object falls to the ground when it is released (post 16.21) and a stretched spring recoils when released (post 16.49). But this can’t be true for the molecules in a… Continue reading 20.26 Boltzmann and other distribution laws

Before you read this, I suggest you read post 17.5 Liquids and gases are both examples of fluids – things that flow into the space available to them (post 16.37). In post 17.5, we saw how the pressure in a liquid increased with depth. Normally, we think of the pressure in a gas as being… Continue reading 20.25 Pressure distribution in fluids

Before you read this, I suggest you read post 20.23. In post 20.23 we saw that, when a gas is compressed, it is subjected to the same pressure in all directions, so that its resistance to compression is given by its bulk modulus, B, defined by B = –Vdp/dV                     (1) (post 20.20) where V is… Continue reading 20.24 Adiabatic compression of a gas

In post 20.20 we looked at isotropic compression of a solid object. In a gas, or a liquid, the pressure acts equally in all directions (post 17.5), so when a gas is compressed it is subjected to isotropic compression. Then resistance to compression is then given by the bulk modulus of the gas (post 20.20).… Continue reading 20.23 Isothermal compression of a gas

In post 20.20, we saw that there was a relationship between the Young’s modulus, E (post 20.2) and the bulk modulus, B (post 20.19) of a material. The relationship is given by E = 3B(1 – 2ν)                     (1) where ν is the Poisson’s ratio (post… Continue reading 20.22 Relationship between Young’s modulus and shear modulus