MCAT Light

Question 1

What type of waves are light waves?

Answer 1

Electromagnetic radiation in which the electric and magnetic fields are perpendicular to each other and to the propagation to the wave.

Question 2

Describe the visible light spectrum

Answer 2

Roy G Biv

Red - 700nm, low frequency, low energy, long wavelength.

Violet - 400nm, high energy, high frequency, short wavelength.

Question 3

Describe UV radiation

Answer 3

In the range of 10nm to 400nm and has 3 subregions: UV-A, UV-B, UV-C

Used in medical treatments.

Question 4

Describe infrared radiation

Answer 4

In the range of 700nm to 1mm and has 3 subregions: near- infrared, mid- infrared, and far- infrared.

Used in imaging techniques, physiotherapy, and laser surgery.

Question 5

Describe X- ray and gamma radiation

Answer 5

They have the highest frequencies and highest energies.
Radiation can cause tissue damage by stripping electrons from atoms.

Used in diagnostic imaging and radiation therapy.

Question 6

How can we represent the energy of an electromagnetic wave?

Answer 6

Through the energy of a photon.

Question 7

Describe the relationship between energy and frequency, wavelength.

Answer 7

Energy is directly proportional to frequency and inversely proportional to wavelength.

Question 8

Photoelectric effect

Answer 8

When EM radiation cause ejection of electrons due to the absorption of EM radiation.

The EM radiation absorbed must be greater than the work function.

Question 9

What happens to the KE to electrons when ejected by photons?

Answer 9

They absorb the photon energy and thus cause an increase in the KE of the electron ejected.

The number of electrons ejected depends on the intensity of the EM radiation and the number of photons incident on to the material.

Question 10

Photoelectric effect

Answer 10

The ejection of electrons when it absorbs electromagnetic energy.

Each electron has an electric potential called the work function. The electromagnetic energy needs to exceed the work function to eject the electron.

hf = K.E.+ W

Question 11

Thin- film interference

Answer 11

The phenomenon of generating multi-colored arrays when light reflects off two semitransparent media.

Incident wave reflects from 1st media but some moves through and reflects off the second. The two waves can interact constructively created multicolored arrays or destructively forming darkness.

The thickness of the media influences the thin- film interference. Anything that distorts the surface thickness affects the interference.