This question is about waves in the electromagnetic (e.m.) spectrum - Edexcel - GCSE Physics - Question 9 - 2022 - Paper 1

To calculate the wavelength ($\lambda$) of the microwaves, we use the formula:

$\lambda = \frac{v}{f}$

where:

• $v$ is the velocity of light ($3.00 \times 10^8$ m/s)
• $f$ is the frequency (2.45 GHz or $2.45 \times 10^9$ Hz)

Plugging in the values:

$\lambda = \frac{3.00 \times 10^8}{2.45 \times 10^9} \approx 0.122 \text{ m}$

Thus, the wavelength is approximately 0.122 m.

Given that the microwave oven is 55% efficient and transfers 42,000 J of energy to the food, we can determine the total energy supplied (E_total) using the efficiency formula:

$E_{efficiency} = \frac{E_{transferred}}{E_{total}}$

Rearranging gives:

$E_{total} = \frac{E_{transferred}}{efficiency}$

Substituting in the values:

$E_{total} = \frac{42,000}{0.55} \approx 76,364 \text{ J}$

Therefore, the total energy supplied to the oven is approximately 76,364 J.

X-rays and radio waves serve different purposes and are produced through different processes:

Uses of X-rays:

• X-rays are primarily used in medical imaging to view the inside of the body. They can help diagnose conditions such as fractures, infections, or tumors.
• X-rays are also used in treatments, such as radiation therapy for cancer.

Uses of Radio Waves:

• Radio waves are used for communication purposes, including television, radio broadcasting, and cell phone signals.
• They are also used in navigation systems like GPS.

Production of X-rays:

• X-rays are produced when electrons in an atom transition between energy levels or when high-energy electrons collide with a metal target, emitting energy in the form of X-rays.

Production of Radio Waves:

• Radio waves are produced by accelerating charges in circuits, often using antennas where current is oscillated, generating waves that propagate through space.

In conclusion, while both X-rays and radio waves are essential in modern applications, they differ significantly in their uses and the mechanisms behind their production.