Everything Science Grade 12

CHAPTER 16. OPTICAL PHENOMENA; PROPERTIES OF MATTER 16.4

efficiency so that the panels can generate as high a current as possible,and create as

much electricity as possible from the sun. But even these smaller electrical currents are

useful in applications like solar-powered calculators.

Exercise 16 - 2

1. Describe the photoelectric effect.


2. List two reasons whythe observation of the photoelectric effect was significant.


3. Refer to Table 16.1:If I shine ultraviolet light with a wavelength of 288 nm onto
   some aluminium foil, what would be the kineticenergy of the emitted electrons?


4. I shine a light of an unknown wavelength onto some silver foil. The light has only
   enough energy to ejectelectrons from the silverfoil but not enough to give them
   kinetic energy. (Refer toTable 16.1 when answering the questions below:)

(a) If I shine the same light onto some copper foil, would electrons be ejected?

(b) If I shine the same light onto some silicon, would electrons be ejected?

(c) If I increase the intensity of the light shining on the silver foil, what happens?

(d) If I increase the frequency of the light shining on the silver foil, what hap-

pens?

More practice video solutions or help at http://www.everythingscience.co.za

(1.) 01mq (2.) 01mr (3.) 01ms (4.) 01mt

16.4 Emission and absorption spectra

ESCHI

Emission Spectra ESCHJ

You have learnt previously about the structure of an atom. The electrons surrounding

the atomic nucleus are arranged in a series of levels of increasing energy.Each element

has its own distinct set of energy levels. This arrangement of energy levels serves as the

atom’s unique fingerprint.

In the early 1900s, scientists found that a liquidor solid heated to hightemperatures

would give off a broad range of colours of light.However, a gas heated to similar tem-

peratures would emit light only at certain specific colours (wavelengths). The reason