Ionising radiation can cause damage to living cells, leading to mutations, cancer, or cell death. It can also affect DNA, potentially causing genetic mutations that may be passed on to future generations.

The decay equation for uranium-238 emitting an α-particle is:

\[ \frac{238}{92} U \rightarrow \frac{234}{90} Th + \frac{4}{2} He \]

Here, uranium-238 decays into thorium-234 by emitting an α-particle, which is a helium nucleus (\(\frac{4}{2} He\)).

The speed of gamma radiation in a vacuum is \(3 \times 10^8 \, \text{m/s}\), which is the speed of light.

The correct matching is:

• Infrared – remote controls and intruder alarms
• Microwaves – satellite television and telephones
• Radio waves – radio and TV communications
• X-rays – medicine and security

To complete the diagram, draw two rays from the object:

1. One ray parallel to the principal axis, which refracts through the lens and passes through the focal point on the other side.
2. Another ray passing through the focal point on the object side, which refracts parallel to the principal axis after passing through the lens.

The point where these two rays intersect after refraction is the location of the real image formed by the lens.

A real image is formed when light rays actually converge at a point, and it can be projected onto a screen. A virtual image, on the other hand, is formed when light rays appear to diverge from a point, and it cannot be projected onto a screen.