IB Physics Emissivity

A tutorial sheet of questions on emissivity is given below.

1. What is the emissivity of a perfect black body?
2. Is emissivity the same as albedo?
3. A metal sphere of radius 2.50 cm is placed in a vacuum and has a surface temperature 523 °C. The intensity of the radiation from the sphere at a distance of 12.0 cm from its centre is 2.37 kW m^-2. Find the emissivity of the sphere.
4. Does emissivity have an effect on the peak wavelength in the radiation spectrum of an object?
5. Determine the peak wavelength in the radiation spectrum of the sphere in question 3.
6. Would a human eye "see" the sphere in question 3?
7. Infra red radiation has a wavelength between 750 nm and 1.0 mm. Visible light has wavelength between 380 nm and 750 nm. By referring to a Planck radiation curve, determine the ratio of the total energy emitted by the sphere as infra red radiation to that emitted as visible light.

IB Physics emf

The term emf is a misunderstood concept. Listed below are a number of possible definitions. Which are correct? What must be added/deleted to make them correct?

1. The voltage of a battery.
2. The potential difference of a battery.
3. The potential difference of the battery when no current is flowing through it.
4. The work done per unit positive charge.
5. The power per unit current.
6. The work done in moving a charge between two points.
7. The work done in moving a +1 C charge at a constant speed along a path in an electric field.
8. The integral of the electric field along the path taken.
9. The line integral of the electric field component parallel to the path taken along the path taken.
10. The work done in moving a +1 C charge at a constant speed around a closed path in an electric field.
11. The emf of a cell is the work done per unit positive charge in going around the circuit.