1. Working as a Physicist

Question 1

What is precision?

Answer 1

Where the spread of data is small
So it doesn’t need to be accurate, but all results have to be close together

Question 2

What is accuracy?

Answer 2

then the result is close to the real value

Question 3

What is a controlled variable?

Answer 3

The variable that is unchanged and constant
E.g amount of sees placed for pants to grow
for an equal test

Question 4

What is an independant variable?

Answer 4

A variable that you manipulate and isn’t influenced by other variables
E.g amount of water for a plant

Question 5

What’s a dependant variable?

Answer 5

A variable that changes due to a change of another variable
E.g size of the plant

Question 6

What are systematic errors?

Answer 6

Affect the accuracy due to the apparatus or faults
- causes results to be too high/ low by same amount

Question 7

How can we reduce systematic errors?

Answer 7

Calibrate apparatus
- identify how far off a scale is
Read the meniscus at eye level, to reduce parallax error

Question 8

What is a meniscus?

Answer 8

The curve at the top of a liquid, the centre of it where it’s straight is the meniscus

Question 9

What is parallax error?

Answer 9

Reading not at eye level makes a parallax error

Question 10

What is a random error?

Answer 10

​Unpredictable variation between measurements that leads to a spread of values about the true value
So they effect precision

Question 11

How do we reduce random errors?

Answer 11

Take at least 3 readings
use computers/ data loggers/ cameras
use appropriate equipment
- with high resolutions, like a micrometer

Question 12

What is a resolution?

Answer 12

The resolution is how precise a price of equipment is
The higher the resolution, the lower the gaps of the instrument
A micrometer has a resolution of 0.1mm
A ruler has 1mm

Question 13

What are the 2 types of uncertainties?

Answer 13

Absolute uncertainty
Percentage uncertainty

Question 14

What is an absolute uncertainty?

Answer 14

An uncertainty given by a fixed quantity
E.g 7±0.6V

Question 15

What is the uncertainty of a measurement?

Answer 15

The uncertainty is half the resolution
E.g resolution=0.1mm
uncertainty=0.05mm

Question 16

How do we find the % uncertainty

Answer 16

(Uncertainty/measurement) x100
E.g ±0.05mm/1.10mm = ±4.5%

Question 17

How do we combine uncertainties to adding/ subtract?
E.g R(1)+R(2)+R(3)

Answer 17

We add their absolute uncertainties
E.g 0.05+0.05+0.05=±0.15V

Question 18

How do we combine uncertainties to multiply/divide?
E.g R=V/I

Answer 18

We add their percentage uncertainties
E.g 0.45%+4.2%=±4.65%

Question 19

How do we combine uncertainties with powers?
E.g area=πr^2

Answer 19

We times the uncertainty by the power
E.g 0.3%x2=0.6%

Question 20

What are prefixes?

Answer 20

prefixes are the multiples before the units
E.g x10^6

Question 21

What are all the prefixes?

Answer 21

Tera, T = x10^12
Giga, G = x10^9
Mega, M =x10^6
Kilo, k =x10^3

deci, d =x10^-1
centi, c =x10^-2
milli, m =x10^-3
micro, µ =x10^-6
nano, n =x10^-9
pico, p =x10^-12
femto, f =x10^-15
atto, a =x10^-18

Question 22

What is homogeneity?

Answer 22

An equation is homogeneous if both sides have identical SI base units
If an equation is not homogeneous, it’s invalid
‘homo’ - same
‘genius’ - kind
E,g mgh=1/2mv^2
kgm^2s^-2=kgm^2s^-2

Question 23

What are SI base units?

Answer 23

System International (SI) units are used globally
They are the fundamental quantities of things in the universe
Everything else is derived from the base units
- so derived units

Question 24

What are the 7 SI base units?

Answer 24

mass, m (kg)
length, L (m)
Time, t (s)
Electric current, I (A)
Thermodynamic temperature, T (k)
Amount of substance, n (mol)
Luminous intensity, L(v) (cd)

Remember ‘smAkmolkg’ to remember the 6 needed

Question 25

How do you derive a unit into base units?

Answer 25

We need to find other formulas that have other units in them
E.g Energy
Energy=Fd, F=ma
Energy=kgms^-2 x m
Energy=kgm^2s^-2

Question 26

If a student takes a measurement, and the reading vary,
Eg 3.2s, 3.2s, 3.3s
What must you take from this?

Answer 26

That the uncertainty is 0.1s
You shouldn’t record the average