Live practice

Each branch receives the full supply voltage and can draw the current required by its own resistance. Each appliance can be switched independently, and failure of one branch does not interrupt the others. Devices of different power ratings can therefore operate correctly.

Blue sky on Earth results from Rayleigh scattering of sunlight by atmospheric molecules. In space there is essentially no atmosphere around the observer, so sunlight is not scattered into the line of sight. Apart from direct luminous objects, the background appears black.

This image occurs only when the object lies inside the focal length, between pole P and focus F. Reflected rays diverge and their extensions meet behind the mirror.

Meiosis, independent assortment and fusion of gametes combine DNA from two parents, producing more genetic variation than cloning. Variation can improve adaptability to disease or environmental change and supplies material for natural selection and evolution. The basic body plan is still preserved by accurate DNA copying.

The junction is a synapse; its physical gap is the synaptic cleft.

Xylem transports water and mineral ions, mainly upward from roots. Phloem transports sucrose, amino acids and other organic solutes between sources and sinks in either direction. Roots, stems and leaves contain continuous vascular bundles of these tissues.

A black deposit is soot, consisting mainly of unburnt carbon. It forms when oxygen is insufficient and the fuel undergoes incomplete combustion.

Copper is more reactive than silver, so it displaces silver from silver nitrate:

The other listed metals are below the metal ion they would need to displace.

Dry slaked lime, calcium hydroxide, is treated with chlorine:

Principle. A closed pipe has fn=(2n−1)v/(4L); an open pipe has fn=nv/(2L).