Homeostasis, Diffusion, Waves, and Converging Lenses

Vocabulary flashcards covering Cambridge IGCSE revision topics in Biology (homeostasis and blood glucose regulation), Chemistry (gas diffusion and relative molecular mass), and Physics (electromagnetic spectrum, longitudinal waves, ultrasound, and converging lenses).

Homeostasis

The maintenance of a constant internal environment.

Set point

The normal or ideal level that the body tries to maintain.

Negative feedback

A process where a change away from the set point causes a response that reverses or opposes the original change.

Insulin

A hormone secreted by the pancreas when blood glucose concentration is too high, causing body cells to take up more glucose and the liver to convert glucose into glycogen.

Glucagon

A hormone secreted by the pancreas when blood glucose concentration is too low, causing the liver to convert glycogen into glucose.

Blood glucose control summary

A table outlining the hormone released, liver effect, and overall blood glucose result when levels are too high or too low.

Diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration as a result of their random movement.

Relative molecular mass ($M_r$) effect on diffusion

The lower the relative molecular mass ($M_r$), the faster a gas diffuses because its particles move faster on average at the same temperature.

Electromagnetic waves properties

Transverse waves that can travel through a vacuum at a constant speed of $3.0 \times 10^8\,\text{m/s}$.

Ultraviolet (UV) radiation

Transverse electromagnetic wave with a shorter wavelength and higher frequency than visible light, used for sterilisation, water disinfection, and security marking.

Longitudinal wave

A wave in which the particles vibrate parallel to the direction of energy transfer.

Compression

A region in a longitudinal wave where particles are close together.

Rarefaction

A region in a longitudinal wave where particles are further apart.

Ultrasound

Sound with a frequency above $20\,000\,\text{Hz}$, which is beyond human hearing.

Converging lens

A lens that is thicker in the middle and thinner at the edges, causing parallel rays of light to converge at the principal focus.

Principal axis

The straight line passing through the optical centre of the lens.

Principal focus ($F$)

The point where rays parallel to the principal axis converge after passing through the lens.

Focal length

The distance from the optical centre of the lens to the principal focus.

Converging lens object positions and image characteristics

A reference table outlining the nature, orientation, and size of an image formed by a converging lens depending on the object position relative to $F$ and $2F$.