Topic 5: Light And The EM spectrum Flashcards
How to draw a ray diagram
To draw a ray diagram (what nathan taught)
Draw a ray from the object to the lens that is parallel to the principal axis (x axis)
Once through the lens, the ray should pass through the principal focus.
Draw a ray that passes from the object through the centre of the lens.
Concave lenses are (3 things)
Same with convex lenses
Concave
Upright
Diminished
Virtual
Convex
Inverted
Diminished
Real
Recall that all electromagnetic waves are
transverse, that they
travel at the same speed in a vacuum
Explain, with examples, that all electromagnetic waves transfer ______ from _____ to _____
energy
source
observer
When we see things, light energy travels from a source to our eyes (observers)
Order of EM from lowest to highest wavelength
Gamma
Xray
UV
Visible light (violet-red)
IR
micro
Radio
Describe the electromagnetic spectrum as _______ from
radio waves to gamma rays and that the radiations within it
can be grouped in order of decreasing wavelength and
increasing frequency
Continuous
Recall that our eyes can only _____ a _____ _____ of
frequencies of electromagnetic radiation
Detect
Limited
Range
Explain the effects of differences in the velocities of
electromagnetic waves in different substances
One effect is refraction/bending of light
The speed of light is different in different materials, and this change in speed causes the wave to change direction.
Explain that all bodies emit radiation, that the intensity and wavelength distribution of any emission depends on their
temperature
All bodies with a temperature above absolute zero emit electromagnetic radiation, and the intensity and wavelength distribution of this radiation are directly related to the body’s temperature. As temperature increases, the intensity of emitted radiation increases, and the peak wavelength of the emission shifts towards shorter wavelengths (higher frequencies).
Explain that for a body to be at a constant temperature
it needs to radiate the same average power that it
absorbs
For a body to maintain a constant temperature, it must radiate the same amount of energy (power) that it absorbs, creating a balance between incoming and outgoing energy. If a body absorbs more energy than it radiates, its temperature will increase; conversely, if it radiates more energy than it absorbs, its temperature will decrease.
Explain what happens to a body if the average power it
radiates is less or more than the average power that it
absorbs
If a body radiates less power than it absorbs, its temperature will increase because it is gaining more energy than it is losing.
Explain how the temperature of the Earth is affected by
factors controlling the balance between incoming
radiation and radiation emitted
The Earth’s temperature is primarily regulated by the balance between incoming solar radiation and outgoing radiation emitted by the Earth. This balance is influenced by several factors, including the amount of solar radiation absorbed and reflected, the concentration of greenhouse gases in the atmosphere, and the Earth’s surface characteristics.
Recall that the potential danger associated with an
electromagnetic wave increases with increasing frequency
High frequency waves cause more damage as they transfer more energy. Ultraviolet waves, X-rays and gamma rays are all types of ionising radiation.
Ionising means that these waves can add or remove electrons from molecules, resulting in the molecules becoming electrically charged (ions).
Describe the harmful effects on people of excessive exposure
to electromagnetic radiation, including:
a microwaves: internal heating of body cells
b infrared: skin burns
c ultraviolet: damage to surface cells and eyes, leading to
skin cancer and eye conditions
d x-rays and gamma rays: mutation or damage to cells in the body
Describe some uses of electromagnetic radiation
a radio waves:
including broadcasting, communications and
satellite transmissions
Describe some uses of electromagnetic radiation
b microwaves:
including cooking, communications and
satellite transmissions
Describe some uses of electromagnetic radiation
c infrared:
including cooking, thermal imaging, short range
communications, optical fibres, television remote controls
and security systems
Describe some uses of electromagnetic radiation
d visible light:
including vision, photography and illumination
Describe some uses of electromagnetic radiation
e ultraviolet:
including security marking, fluorescent lamps,
detecting forged bank notes and disinfecting water
Describe some uses of electromagnetic radiation
f x-rays:
including observing the internal structure of objects,
airport security scanners and medical x-rays
Describe some uses of electromagnetic radiation
g gamma rays:
including sterilising food and medical
equipment, and the detection of cancer and its treatment
Recall that radio waves can be ______ by, or can themselves _______ ______ in electrical circuits
Produced
Induce
Oscillations
Recall that changes in atoms and nuclei can
a generate radiations over a wide frequency range
b be caused by absorption of a range of radiations
Explain TIR and when it occurs
When the angle of incidence is above the critical angle (angle where the angle of refraction is 90*), instead of the ray leaving the more dense medium it reflects back inside the medium
It only occurs when:
light travels from a dense medium to a less dense medium e.g. from glass to air;
the angle of incidence in the dense medium is greater than the critical angle;
if the angle of refraction in the air becomes 90°, the angle of incidence in the glass is called the critical angle;
if the angle of incidence in the glass is greater than the critical angle,
total internal reflection occurs.
