Everyday Science Mixed Quiz 3: Light, Heat, Force and Life, WBPSC Clerkship GS

Red has the longest wavelength in visible light (about 700 nm) and violet the shortest (about 400 nm). Because its wavelength is long, red light is scattered the least by air. That is why red is used for danger signals: it can be seen from far away.

Sunlight is scattered by gas molecules and dust in the atmosphere. Blue light, with its short wavelength, is scattered the most, so blue light reaches our eyes from every direction. The sea looks blue partly because it reflects the sky and partly because water absorbs red light, not the other way round.

A concave mirror gives an erect, enlarged image when the object is close, so dentists use it. A convex mirror always gives a smaller image but a wide field of view, which is why a vehicle rear-view mirror is convex. A lens refracts light instead of reflecting it, so it is not a mirror.

Most of the space between the Sun and the Earth is empty, so neither conduction nor convection is possible. Heat arrives directly as electromagnetic waves, which is radiation. Conduction happens in solids and convection in liquids and gases.

The trapped steam raises the pressure inside the cooker, so the boiling point of water goes above 100°C. Food cooks faster in hotter water. In the hills the air pressure is low, so water boils at a lower temperature and cooking is slower.

Vitamin A is needed to make the light-sensitive pigment in the retina. Without it a person cannot see in dim light, which is night blindness. Vitamin A is found in carrot, papaya, yellow and green vegetables, liver and eggs.

Vitamin D helps the body absorb calcium and phosphorus. Without it a child's bones become soft and bend, which is rickets. Sunlight makes vitamin D in the skin, so it is also called the sunshine vitamin.

Magnesium sits at the centre of the chlorophyll molecule. Iron is found in haemoglobin in human blood, not in chlorophyll. With chlorophyll a plant absorbs sunlight and makes food by photosynthesis.

Dengue is a viral disease spread by the Aedes mosquito. Malaria is caused by a protozoan, Plasmodium, carried by the Anopheles mosquito. Typhoid and cholera are bacterial diseases.

When water freezes its volume increases, so its density falls (about 0.92 g/cm³). Water has a density of about 1 g/cm³, so the less dense ice floats. That is why in cold countries only the top of a lake freezes and fish survive in the water below.

The SI unit of force is the newton (N): the force needed to give a mass of 1 kg an acceleration of 1 m/s². The joule is the unit of work and energy, the watt of power and the pascal of pressure.

To convert Fahrenheit to Celsius, subtract 32 and multiply by $\frac{5}{9}$: $\frac{5}{9} \times (98.6 - 32) = \frac{5}{9} \times 66.6 = 37$. So normal body temperature is 37°C. The values 36°C and 38°C are close, but 38°C would count as fever.

The passengers move along with the bus. When the bus stops suddenly their bodies try to keep moving, so they lean forward. This property of matter is inertia, and it comes from the first law of motion.

The two blades of scissors turn about a fixed point, called the fulcrum, so scissors are a lever. In fact scissors are two levers joined together. A sloping ramp is an inclined plane, while the screw and pulley are different simple machines.

Air pressure is measured with a barometer. A thermometer measures temperature, a hygrometer the humidity of the air and an ammeter electric current. A sudden fall in the barometer reading warns of a storm.

Diamond is a form of carbon in which every atom is firmly bonded to four others, so it is the hardest natural substance. Graphite is also carbon, but its layers slide over each other easily, so it is soft.

Soda water is made by dissolving carbon dioxide in water under pressure. When the bottle is opened the pressure drops and the gas escapes as bubbles. The gas gives a slightly sour taste because it forms carbonic acid in water.

A potato is a modified stem called a tuber. New shoots grow from its eyes, which is a feature of stems. Carrot, radish and sweet potato, however, are modified roots.

The red cells of group O carry neither the A nor the B antigen, so they do not usually cause a reaction in people of other groups. That is why O is called the universal donor. Group AB has no antibodies, so it can receive blood of every group and is called the universal recipient.