Question 1: Define 'emission' in the context of black body radiation.

Answer: Emission refers to the process by which a black body emits electromagnetic radiation as a result of its temperature.

Question 2: Explain why hotter objects emit more radiation across all wavelengths.

Answer: Hotter objects have higher thermal energy, which increases the number of photons emitted at all wavelengths, resulting in more radiation overall.

Question 1: Calculate the energy of a photon emitted by a black body at a wavelength of 500 nm. (Use Planck's constant h = 6.626 × 10⁻³⁴ Js, speed of light c = 3.00 × 10⁸ m/s).

Answer: E = hc/λ; E = (6.626×10⁻³⁴ Js)(3.00×10⁸ m/s) / 500×10⁻⁹ m = 3.97×10⁻¹⁹ J

Question 2: A black body at 3000 K emits radiation. Using Wien's Law, estimate the wavelength at which the emission peaks. (Wien's constant b = 2.898×10⁻³ m·K).

Answer: λ_max = b / T; λ_max = 2.898×10⁻³ m·K / 3000 K = 9.66×10⁻⁷ m (or 966 nm)

Question 1: Describe a simple experiment to demonstrate black body radiation emission. Include the variables that can be controlled and safety precautions.

Answer: One experiment involves heating a metal filament (like tungsten) until it glows, and observing the spectrum of emitted light with a spectroscope. Variables to control include temperature (by adjusting current) and environment (ensuring an inert atmosphere). Safety precautions include wearing eye protection, avoiding contact with hot equipment, and ensuring proper insulation to prevent electric shocks.

Question 1: A star emits maximum radiation at a wavelength of 480 nm. Using Wien's Law, estimate its surface temperature.

Answer: T = b / λ_max; T = 2.898×10⁻³ m·K / 480×10⁻⁹ m ≈ 6038 K

Question 2: An object with a temperature of 2500 K emits radiation. Describe how its emission spectrum compares with that of a 6000 K object.

Answer: The 2500 K object emits primarily in the infrared and visible spectrum with a peak at longer wavelengths, appearing red, while the 6000 K object emits more strongly at shorter wavelengths, appearing whiter or bluish, with a higher overall emission.

Question 1: Explain how the emission spectrum of a black body changes as its temperature increases. (6 marks)

Answer: As the temperature of a black body increases, its emission spectrum shifts towards shorter wavelengths, meaning the peak wavelength decreases. The total emitted radiation also increases significantly, following Stefan-Boltzmann law. The spectrum becomes more intense and broader, with a higher proportion of high-energy photons emitted.

Question 1: Describe how understanding black body emission is crucial in designing thermal imaging cameras.

Answer: Thermal imaging cameras detect infrared radiation emitted by objects based on their temperature. Understanding black body emission allows engineers to calibrate these devices accurately, enabling them to measure temperature differences without contact.

Question 2: Explain the importance of emission principles in the development of solar thermal collectors.

Answer: Solar thermal collectors rely on absorbing solar radiation and emitting infrared radiation efficiently. Understanding emission helps optimise materials and surface treatments to maximise heat absorption and minimise heat loss through radiation.