Knock out the photoelectric myths

Exercise and reference answers

Questions

1. Question

   Three of these claims about photoelectric emission are false.

   Choices

   1. Explanation

      Extra photons add to the count, never to the energy of one electron.

      Item

      Brighter light raises electron energy.

   2. Item

      A brighter beam ejects more electrons.

      Correct

      Yes

   3. Explanation

      Below the threshold no photon carries enough energy, however many arrive.

      Item

      Bright light works below the threshold.

   4. Explanation

      Ejection is instant, well under a billionth of a second.

      Item

      Emission needs a long build up first.

2. Question

   Three of these descriptions of the stopping potential are false.

   Choices

   1. Explanation

      That is saturation, the opposite end of the same graph.

      Item

      The voltage that collects every electron.

   2. Explanation

      Threshold names a frequency, not a potential.

      Item

      The frequency below which none escape.

   3. Item

      Retarding voltage that zeroes the current.

      Correct

      Yes

   4. Explanation

      Ionisation is an atomic quantity, not surface emission.

      Item

      The energy that frees a bound electron.

Instructions

Tap away the three false claims in each set about photoelectric emission.

Explanation