Transcript Fundamental & Derived Units - Red Hook Central School District

Fundamental & Derived Units
SI = system international
Agreed upon fundamental/base
units & definitions.
7 Base/Fundamental Units
• Unit
• Meter
Symbol
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• Kilogram
• Second
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• Ampere
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• Kelvin
• Mole
• Candela
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mol
cd
Dimension
d light trav in vacuum
in frac of sec
amt of pt/irridium alloy.
e- vibrations during E
transition Cs.
current in parallel
wires 1m apart that
produces certain F.
frac. triple pt water.
_________________.
intensity of light.
Derived Units: Combos of base
Mechanics – motion, force, matter. All units
derived from kg, m, s.
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What are some examples of derived units:
Density
Velocity
Force
Momentum
volume
Remind yourselves of the metric
prefixes.
See Hamper pg 6.
1. What are the base units of Joules?
kg m2 s-2.
2. What unit is a C/s?
• Ampere
3. What quantity is represented by
the base unit below?
kg m2
s3 A
Volts
4. Break down the unit W (ohm) into
base units.
• kg m2 s-3 A-2.
Order of Magnitude & Estimation
• Physics must explain the very large & the very
small.
Scientific Notation
• Expresses values as powers of 10
• The number of atoms in 12 g of 12C?
• ~ 600 000 000 000 000 000 000
• ~ 6 x 1023.
60 x 1022 what’s the difference?
The power of 10 of a number is its order of
magnitude.
• Useful to estimate very large & small values.
• Ex: 10n = 6 x 1023
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n = order of mag.
Solve for n.
Take the log of 6 x 1023.
n = 23.7
Round to whole number
n = 24.
5. Find the following order of mag.
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1m
4 000 N
80 000 J
5 x 10-10 m
14 billion years
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3.6 or 4
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-9
1.4 x 1010 so 10.
6. What is the order of mag of the mass
of an electron in kg?
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~ 9 x 10-31 kg.
~ 10 – 31 kg.
~ 1 x 10-30 kg.
So -30.
7. The universe ~10
25
m across.
It is ~ 15 BY old.
• How many seconds is that?
Estimate to within an order of
mag.
~ 10
18
seconds
8. Diameter:
Atom ~ 10 – 10 m
Nucleus ~ 10 – 15 m
What is the ratio between the two to
an order of magnitude?
10 5.
9. The smallest time interval that can be
measured is the time it takes light to
traverse the nucleus. Estimate that time.
• t = d/v
• t = (10-15m)/(3x108 m/s)
• ~ 10 -24 s
Wavelength of light few hundred nm (400 – 700)
Frequency light ~ 4 – 8 x 1014 hz.
• Try to memorize the previous quantities.
• See list on pg 1 in Kerr.
Hwk: Read Hamper 1 – 6.
Do pg 3 - 6 # 1 – 7
Show work or write word.
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Write your whole name.
Date.
Assignment.
Label questions.
Show work.
Make estimations in groups outside.
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