General Science Mixed Quiz: Set 202

Thrust is a force and impulse is force multiplied by time, so thrust divided by impulse has the unit 1/second (s⁻¹), which is the unit of frequency.

Heavy water is D2O, in which both hydrogen atoms are deuterium, the isotope whose nucleus has one proton and one neutron, so its molecular mass is twenty instead of eighteen.

By the conservation of momentum, the pistol moves back with 3 m s⁻¹, and the minus sign shows it moves opposite to the bullet.

Gustatory receptors are the receptors of taste, and they lie in the taste buds of the tongue, which sit mostly on small projections called papillae; they are stimulated by chemicals dissolved in saliva and send impulses to the brain.

Using kinetic energy = ½mv² with the mass in kilograms gives a speed of exactly 10 m/s. First convert the mass to SI units: 2000 g = 2 kg.

When cells are joined in parallel all their positive terminals are connected together and all their negative terminals together, so each cell is across the same two points and the voltage of the combination is the voltage of one cell, that is 12 volts.

This follows from Newton's third law and his law of gravitation. Newton's law of gravitation gives the force between two bodies as F = Gm₁m₂/r².

Lumps of calcium carbide hidden in a crate of mangoes react with the moisture in the air and release acetylene gas, which forces the fruit to colour quickly, though the pulp inside stays unripe and tasteless.

A system whose walls let no heat pass in or out is called adiabatic, so any change in its state happens with zero heat exchange (Q = 0).

Egg white is mostly water and protein, and heat denatures these proteins so that they set into an opaque white solid.

The bulb of a headlight is placed at the principal focus of a concave mirror, so the reflected light leaves as a strong beam of parallel rays that reaches far down the road.

Ampere-turns per metre, written AT/m, is the unit of magnetic field strength, because H is the magnetomotive force set up per unit length of the magnetic path.

SONAR sends out ultrasonic pulses and times their echo from underwater objects. SONAR stands for Sound Navigation and Ranging.

A person with Down syndrome carries three copies of chromosome 21 instead of two, a condition called trisomy 21, so the total chromosome number is 47 rather than 46.

Resistivity is a property of the material itself, so changing the length of a copper wire does not change it.

A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.

The Swedish chemist Berzelius proposed around 1813–1814 that each element be written with one or two letters taken from its name, the system still used today.

Slaked lime on the wall slowly absorbs carbon dioxide from the air and turns into a thin, shiny layer of calcium carbonate.

On heating, sodium bicarbonate releases carbon dioxide gas, whose bubbles make dough rise and turn cakes and bread soft and spongy.

The filament of an incandescent bulb must glow white-hot without melting, and tungsten has the highest melting point of all metals, about 3,400 °C. An incandescent bulb works by the heating effect of electric current: the thin coiled filament gets so hot, around 2,500 °C or more, that it gives…