5. Select the correct definition for the electron volt.
A) The energy emitted by an electron per volt.
B) The work done on an electron when accelerating through 1 volt.
C) The voltage of an electron in a magnetic field.
D) The voltage gained by an electron over a metre of voltage.

15. A photon has a frequency of 4.5 ×10^{14} Hz and is incident on a metal plate with a work function of 7.7 eV. How many electrons are emitted per second from the plate?
A) 4.5 ×10^{14}
B) 7.7
C) 0
D) 7.5 × 10^{18}


20.An open-closed tube is used to measure the speed of sound using a frequency of 299 Hz. A second tube is used which is measured to be 34 cm longer and resonates with the next harmonic. Calculate the speed of sound in the tube.​