Week 4 revision

Pions are particles created in the upper atmosphere by cosmic rays from the Sun. Pions decay with an average rest lifetime of 26 nanoseconds (ns). In which frame of reference will the rest lifetime be correctly observed?

• in Earth’s frame

• in the frame of the high-energy source of each pion

• in each pion’s own frame

• in any inertial frame

Consider one particular pion approaching Earth at a speed of 0.98c. It decays 26 ns after it is formed in its own frame of reference. How long did the pion exist in Earth’s frame of reference?

• 26 ns

• 130 ns

• 650 ns

• 5.2 ns

The sun has a surface temperature of 5573 K. Assuming the sun radiates energy like a black body, calculate the wavelength of its peak energy radiation.

• 0.53 nm

• 5300 nm

• 530 nm

• 53 nm

The photoelectric graph in the figure can be used to determine the work function of two unknown metals A and B. Deduce what the gradient of the graph represents.

• stopping potential

• threshold frequency

• Planck's constant

• intensity

Determine the wavelength, in metres, of a photon with energy of 3.5 eV.

• 1.18 × 10^−15

• 1.2 × 10^−6

• 5.67 × 10^−26

• 3.5 × 10^−7