General Science Mixed Quiz: Set 87

A microphone turns sound into an electrical signal, and a speaker turns an electrical signal back into sound. Both are transducers, devices that change energy from one form to another.

A beam seen from the side is visible only because tiny particles send some of its light sideways. Light travelling in a straight line cannot enter our eyes unless something redirects it towards us.

Chemical energy is the energy stored in the bonds that link atoms together in molecules. When a chemical reaction breaks old bonds and forms new ones, this stored energy is released or absorbed.

Rotational kinetic energy is ½Iω², and the ring has the larger moment of inertia. For a thin ring about the axis through its centre and perpendicular to its plane, all the mass sits at distance R, so I = MR².

Red blood cells far outnumber both platelets and white blood cells. A microlitre of healthy adult blood holds about 4.5 to 5.5 million red blood cells, about 1.5 to 4.5 lakh platelets and only about 4,000 to 11,000 white blood cells.

One parsec equals about 2,06,265 astronomical units, which rounds to 2 × 10⁵ A.U.

Cancer is uncontrolled cell division that follows the loss of the checks that normally govern growth. Normal cells divide only when signalled and stop when they touch neighbouring cells, a property called contact inhibition.

An ion-exchange resin or zeolite swaps the calcium and magnesium ions that cause permanent hardness for sodium or hydrogen ions.

Chlorophyll is held in the chloroplasts, the green plastids of leaf cells where photosynthesis takes place. A chloroplast is a double-membrane organelle.

During a hard sprint the muscles run short of oxygen and switch to anaerobic respiration, which leaves lactic acid behind.

Mendel worked out the laws of inheritance by crossing garden pea plants, Pisum sativum. Gregor Johann Mendel, an Austrian monk, carried out his hybridisation experiments between 1856 and 1863 in the monastery garden at Brno and published the results in 1866.

A normal umbilical cord contains two arteries and one vein, three blood vessels in all. The umbilical cord joins the developing foetus to the placenta.

Hydrogen, nitrogen, oxygen and carbon dioxide all exist as gases at about 25 °C and normal atmospheric pressure. Hydrogen boils at about −253 °C, nitrogen at −196 °C and oxygen at −183 °C, so all three are gases at room temperature.

The hepatitis B vaccine was the first vaccine made by recombinant DNA technology.

A floating body is stable only when its metacentre lies above its centre of gravity. When a floating body tilts slightly, its centre of buoyancy, the centre of the displaced liquid, shifts to one side.

Guava is the classic jam fruit because it is rich in both pectin and acid, the two things a jam needs to set into a firm gel.

The eye changes the focal length of its lens to focus and changes the size of its pupil to control the light.

Common solder is an alloy of lead (Pb) and tin (Sn), often in a ratio close to 40:60. Solder is used to join metal parts, especially wires and components in electrical circuits.

Biogas is mostly methane, with carbon dioxide as the second gas and only small amounts of nitrogen and others. Biogas forms when cattle dung, kitchen waste or crop residue is broken down by anaerobic bacteria, that is, without air, inside a digester.

A single-celled organism has no organs at all; the one cell takes in food through its surface or by forming temporary structures.