- Derived electric unit - unit of electrical resistance - if a potential of 1 volt is applied across a conductor and produces a current of 1 ampere, the resistance of this conductor is 1 ohm V=IR, R=V/I (Ohms Law)

- derived electrical unit - unit of charge or quantity of electricity - 1 coulomb is the quantity of electricity transported in 1 second by a current of 1 ampere Coulomb = ampere x time

- derived electrical unit - unit of capacitance - a capacitor has 1 farad of capacitance if a potential difference of 1 volt is present across its plates, when a charge of 1 coulomb is held by them Q=CV

SI Units Flashcards by Molly Wilkins

SI unit for time

Seconds

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SI Unit for length

Meters

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SI. unit for amount of substance

Moles

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SI. unit For electric current

Amperes

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SI. unit For luminous intensity

Candela

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SI. unit For temperature

Kelvin

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SI. unit For mass

Kilograms

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How many base SI units are there?

7 (SMMACKK)

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Origin of a second

Duration of time for caesium-133 atom to oscillate a certain number of times (9,192,631,770) I.e. it’s based on the frequency of radiation emitted from caesium-133

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Origin of a metre

Length that light travels in a vacuum in 1/300,000,000 of a second

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Origin of a mole (SI unit)

Amount of substance which contains as many elementary particles as there are atoms in 0.012kg (12g) of carbon-12

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Origin of ampere (SI unit)

An ampere is the current which produces a force of 2x10^-7 newtons per metre between 2 parallel conductors 1metre apart in a vacuum

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Origin of Candela (SI unit)

The luminous intensity of a perfect black body at a specified high temperature
I.e. monochromatic light

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Origin of kelvin (SI unit)

1/273.16 of the thermodynamic triple point of water

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What is the triple point of water

The point at which water, water vapour and ice all exist in equilibrium (relevant to kelvin definition)

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Origin of kilogram (SI unit)

The mass of the prototype kilogram held in sevres France

*NOTE- the only base SI unit based on physical quantity . Others based on physical properties of defined systems which are reproducible over time. Risk of prototype degrading

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How many derived electrical units are there?

(Volt, ohm, coulomb, farad)

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What are the 4 electrical derived units

Volt, ohm, coulomb, farad

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Define volt

Derived electrical unit of electrical potential. One volt is the difference of electrical potential between two points of a conductor carrying constant current of 1 ampere, when the power dissipated between these points is 1 watt

Watt = volt x ampere
Volt = watt/ampere

SI base units as 1 V = 1 kg m2 s-3 A -1 (one-kilogram meter squared per second cubed per ampere).

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Define Ohm

Derived electric unit
unit of electrical resistance
if a potential of 1 volt is applied across a conductor and produces a current of 1 ampere, the resistance of this conductor is 1 ohm
V=IR, R=V/I (Ohms Law)

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Define coulomb

derived electrical unit
unit of charge or quantity of electricity
1 coulomb is the quantity of electricity transported in 1 second by a current of 1 ampere

Coulomb = ampere x time

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Define Farad

derived electrical unit
unit of capacitance
a capacitor has 1 farad of capacitance if a potential difference of 1 volt is present across its plates, when a charge of 1 coulomb is held by them

Q=CV

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What is Volt a unit of?

Electrical potential

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What is Ohm a unit of?

Electrical resistance

What is coulomb a measure of?

Charge or quantity of electricity

What is Farad a unit of?

Capacitance

How many derived non-electrical units are there

7 (Hertz, newton, pascal, joule, electronvolt, watt, Celsius)

What is Hertz a unit of?

Frequency - one hertz is a frequency of one cycle per second

What is measured in Newtons?

Force

Define Newton

- derived non-electrical unit - force - 1 newton = the force which gives a mass of 1 kg the acceleration of 1 meter per second per second 1kg.m/s^2

What is measured in Pascals?

Pressure

Define Pascal

- derived non-electrical unit - a pascal is the pressure of 1 newton per square Metre 1 kilogram per metre second squared (1kg/ms2) or 1 newton per metre squared (1N/m2)

What is measured in joules

Energy or work

Define 1 joule

- Derived non electrical unit - unit of energy or work -amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force. 1J=1N.m 1J= kg.m^2.s^-2

What is measured in electronvolt

ElectroMagnetic radiation

Define electronvolt

- derived non electrical unit - an electron volt is the energy required to move one electron through a potential difference of 1 volt in a vacuum and equals 1.6x10^-19 joules

What is measured in watts?

Power

Define Watt

- derived non electrical unit - unit of power - power is the rate of energy expenditure so 1 watt = 1 joule per second

What is measure in celsius

Temperature

Define celsius

- derived non electrical unit - unit of temperature - the size of 1 degree Celsius = 1 degree kelvin - the relationship is 1 Celsius = minus 273.15 Kelvin

What is 1 Celsius in Kelvin?

Minus 273.15

What is 1 kilopascal in mmHg?

7.5mmHg

What is 1 kilopascal in cmH2O?

10.2cmH2O

What is 1cmH20 in pascals?

98 pascals

What is 1 atmosphere in kilopascals

101.325 KPa

How many joules is 1 calorie equal to?

4.18

How many newtons does 1kg weight equal?

9.81 newtons

What prefix denotes 10^-12 of a unit?

Pico-

What prefix denotes 10^-9 of a unit?

Nano-

What prefix denotes 10^-6 of a unit?

Micro-

What prefix denotes 10^-3 of a unit?

Milli-

What prefix denotes 10^6 of a unit?

Mega

What prefix denotes 10^3 of a unit?

Kilo

What prefix denotes 10^9 of a unit?

Giga

When expressed in SI units what is standard temperature and pressure

273.15 kelvin (equivalent 0 Celsius) and 101.325 kPa (equivalent 1 bar, 1 atmosphere and 750mmHg)

What is avogadros hypothesis?

- States that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. - the molecular weights of gases may be different but avogadros hypothesis states the number of molecules will be the same therefore more useful to express quantity if gas in terms of molecules - which is mole

What is avogadros number?

-The number of particles there are in 0.012kg of carbon-12 and therefore the number of particles in a mole - the number is 6.022x10^23

What is the volume occupied by 1 mole of gas at standard temp and pressure?

- 22.4L - one mole of any gas will occupy the same volume at the same temp and pressure (avogadros hypothesis)

In thermodynamics what is the triple point of a substance?

The temperature and pressure at which the 3 phases of that substance co-exist in thermodynamic equilibrium

What is the triple point of water?

273.16 kelvin (0.01 Celsius) 611.73 pascals

Denote Newtons in base units

Kg/m/s^2 (Newtons are product of mass (kg), multiplied with acceleration (meters per second per second squared))

Denote Joules in SI units (base)

Joules = force x distance Force = newton (expressed as kg.m.s^-2 Therefore Joules is simplified to kgm^2/s^2

What is the SI unit for pressure?

Pascal

1 atmosphere = how many bar?

1 bar

Convert 1 bar to kPa?

1 bar = 101.3 kPa

Convert 1 bar to kPa?

1 bar = 101.3 kPa

Convert 1 atmosphere to mmHg

1 atm = 760 mmHg

Convert 1 atm to cm H2O

1 atm = 1020 cmH2O

Convert 1 atm to cm H2O

1 atm = 1020 cmH2O

Convert 1 atm to PSI

1 atm = 14.69 PSI

What is SI unit for magnetic flux?

Weber (Wb)

What is SI unit for magnetic flux?

Weber (Wb)

What is SI unit for magnetic flux density?

Tesla (T) 1 T = 1Wb/m2