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Magnification, Refraction and Snell’s Law. Warning – Lots of Math Required for this Lesson! SNC2D. Review Significant Digits. Non-zero digits are always significant! Zeroes placed before other digits are not significant; 0.046 has two significant digits - PowerPoint PPT Presentation
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Magnification, Refraction and Snell’s Law
Warning – Lots of Math Required for this Lesson!
SNC2D
Review Significant DigitsNon-zero digits are always significant!Zeroes placed before other digits are not
significant; 0.046 has two significant digitsZeroes placed between other digits are
always significant; 4009 kg has four significant digits
Zeroes placed after other digits but before a decimal point are NOT significant; 7600 has two significant digits.
Zeroes placed after other digits but after a decimal point are significant; 7.90 has three significant digits
Review of Scientific Notation!4.5 x 10-4 means…
5.6 x 105 means…
the decimal place is moved to the LEFT 4 places
= 4.5 x 10-4 means 0.00045
the decimal place is moved to the RIGHT 5 places
= 5.6 x 105 means 560 000
Converting to Scientific Notation
When writing in scientific notation we need to be aware of the significant digits. This will determine the first number in our term.
Example 1: 546 000 is written as 5.46 x 105
Example 2: 0.0073 is written as 7.3 x 10-3
Example 3: 5008 is written as 5.008 x 103
MagnificationMagnification is the measure of how much
larger or smaller an image is compared with the object itself.
It is expressed as a ratio of height of the image (hi) to the height of the object (ho) .
• M = hi / ho
It can also be determined by taking the ratio of the distance from the image (di) to the mirror and the distance from the object (do) to the mirror
• M = di / do
Magnification Cont’dRemember to use the same units of
measurement in each ratio!
Your final answer will not include any units because they end up cancelling each other out.
If the Magnification factor is greater than 1, the image will be bigger than the object.
If the Magnification factor is less than 1, the image will be smaller than the object.
Magnification Examples
Example 2: A concave mirror creates a virtual image of a candle flame that is 6 cm high. If the magnification of the mirror is 2.5, what is the height of the candle flame?
We are given height and magnification… M = hi / ho rearrange to get the formula… ho = hi / M = 6 cm / 2.5 = 2.4 cm
Example 1: An object is placed 60 cm from a concave mirror. An image is produced 45 cm away. What is the magnification?
We are given distance… M = di / do = 45 cm / 60 cm = 0.75 or 7.5 x 10-1
RefractionRefraction - The bending of light rays as they
pass through two different media (plural for medium)
Light travels very fast - 3.0 x 108 m/s in a vacuum
Light travels slower when it is moving through a medium (air, water, carbon dioxide, table salt, etc.)
Refraction occurs when light Enters a medium and also when it Leaves a medium.
Index of RefractionThe amount by which a transparent medium
decreases the speed of light is called refraction.
The larger the refractive index, the more the medium decreases the speed of light
Speed of light in a vacuum is 3.0 x 108 m/s. This is the fastest that light can travel, therefore it is given a Refractive Index of 1.00.
Table 11.5 Index of Refraction
Page 437 in your textbook!
Index of Refraction FormulaSpeed of light in a vacuum is denoted with a small
letter c
Speed of light in a medium is denoted with a small letter v
The Refractive Index is denoted with a small letter n
The formula we use for index of refraction is n = c / v
In words: The index of refraction is equal to the speed of light in a vacuum divided by the speed of light in the medium
Index of Refraction ProblemsExample 1: The speed of light in leaded
glass is 1.66 × 108 m/s. What is the index of refraction of this type of glass?
n = c / v where c = speed of light in a vacuum = 3.0 x 108 / 1.66 x 108 = 3.0 x 108 m/s = 1.8 v = 1.66 x 108 m/s (given)
n = looking for
Therefore, the index of refraction for leaded glass is 1.8.
Index of Refraction ProblemsExample 2: What is the speed of light
through sapphire?
n = c / v where c = speed of light in a vacuum 1.77 = 3.0 x 108 / v = 3.0 x 108 m/s 3.00 x 108 / 1.77 = v v = looking for 1.69 x 108 m/s = v n = 1.77 (table from pg. 435)
Therefore, the speed of light through sapphire is 1.69 x 108 m/s
DispersionAs white light enters a water droplet, each
wavelength of light gets refracted at slightly different angles.
The light gets refracted twice:Once when it enters the water dropletOnce when it leaves
Introduction to Snell’s Law
If the light strikes the surface of the water at an angle, that part of the light beam that enters first will slow down first.
1.003
1.61
Introduction to Snell’s Law
When light travels from air, with a low refractive index, into water, with a higher refractive index, it bends toward the normal
When light travels from a higher refractive index medium into a lower refractive index medium, it bends away from the normal
The angle of incidence, θi, and the angle of refraction, θR, are measured from the normal.
Introduction to Snell’s Law
Snell’s LawSnell’s law is a formula that uses values for
the index of refraction to calculate the new angle that a ray will take as a beam of light strikes the interface between two media:
n1sinθ1 = n2sinθ2
The indices of refraction of two different media are indicated as n1 and n2 and the angles of incidence and the angle of refraction are indicated as θ1 and θ2
Snell’s Law ExamplesExample 1: When light passes from air into water
at an angle of 60° from the normal, what is the angle of refraction?Solution:
Snell’s Law ExamplesExample 2: In an experiment, a block of cubic zirconia is placed
in water. A laser beam is passed from the water through the cubic zirconia. The angle of incidence is 50°, and the angle of refraction is 27°. What is the index of refraction of cubic zirconia?
Solution:
Seatwork QuestionsPage 424 – 2 questions from EACH sectionPage 425 – 2 questions from EACH sectionPage 438 – All Practice Questions (except for
the two we have already covered)Page 441 – Practice Questions #1,2,3Page 442 – Practice Questions #1,2,3