Working as a Physicist

Question 1

Mass

Answer 1

Kilogram (kg)

Question 2

Length

Answer 2

Metre (m)

Question 3

Time

Answer 3

Second (s)

Question 4

Current

Answer 4

Ampere (A)

Question 5

Temperature

Answer 5

Kelvin (K)

Question 6

SI Units

Answer 6

SI units are the fundamental units which are used alongside the base SI quantities.

Question 7

Amount of substance

Answer 7

Mole (mol)

Question 8

Luminous intensity (brightness of light)

Answer 8

Candela (cd)

Question 9

Tera

Answer 9

10x12

Question 10

Giga

Answer 10

10x9

Question 11

Mega

Answer 11

10x6

Question 12

Kilo

Answer 12

10x3

Question 13

Centi

Answer 13

10x-2

Question 14

Milli

Answer 14

10x-3

Question 15

Micro

Answer 15

10x-6

Question 16

Nano

Answer 16

10x-9

Question 17

Pico

Answer 17

10x-12

Question 18

Femto

Answer 18

10x-15

Question 19

Estimation

Answer 19

Estimation is a skill physicists must use in order to approximate the values of physical quantities,
in order to make comparisons, or to check if a value they’ve calculated is reasonable.

You can find an estimate by rounding your values up or down, as appropriate, and carrying out
any calculation as you would normally do.

Question 20

Limitation of physical measurements

Answer 20

Random errors affect precision, meaning they cause differences in measurements which causes
a spread about the mean. You cannot get rid of all random errors.
An example of random error is electronic noise in the circuit of an electrical instrument.

Question 21

To reduce random errors:

Answer 21

Take at least 3 repeats and calculate a mean, this method also allows anomalies to be
identified.
. Use computers/data loggers/cameras to reduce human error and enable smaller
intervals.
. Use appropriate equipment, e.g a micrometer has higher resolution (0.1 mm) than a ruler
(1 mm).

Question 22

Systematic errors

Answer 22

Systematic errors affect accuracy and occur due to the apparatus or faults in the experimental
method. Systematic errors cause all results to be too high or too low by the same amount each
time.
An example is a balance that isn’t zeroed correctly (zero error) or reading a scale at a different
angle (this is a parallax error).

Question 23

To reduce systematic error:

Answer 23

Calibrate apparatus by measuring a known value (e.g. weigh 1 kg on a mass balance), if
the reading is inaccurate then the systematic error is easily identified.
. In radiation experiments correct for background radiation by measuring it beforehand and
excluding it from final results.
. Read the meniscus (the central curve on the surface of a liquid) at eye level (to reduce
parallax error) and use controls in experiments.

The uncertainty of a measurement is the bounds in which the accurate value can be expected to lie e.g. 20C ± 2°C, the true value could be within 18-22C

Question 24

Absolute Uncertainty -

Answer 24

uncertainty given as a fixed quantity e.g. 7±0.6 V

Question 25

Percentage Uncertainty

Answer 25

uncertainty as a percentage of the measurement e.g. 7±8.6% V

Question 26

To reduce percentage uncertainty

Answer 26

To reduce percentage uncertainty, you can measure larger quantities.

Question 27

Resolution and Uncertainty

Answer 27

Readings are when one value is found e.g. reading a thermometer, measurements are when the difference between 2 readings is found, e.g. a ruler (as both the starting point and end point are judged).

Question 28

The uncertainty in a reading

Answer 28

± half the smallest division, e.g. for a thermometer the smallest division is 1C so the uncertainty is ±0.5C.

Question 29

The uncertainty in a measurement is

Answer 29

The uncertainty in a measurement is at least ±1 smallest division, e.g. a ruler must include both the uncertainty for the start and end value, as each end has ±0.5mm, they are added so the uncertainty in the measurement is ±1mm.

Question 30

Reducing Uncertainty

Answer 30

You can reduce uncertainty by fixing one end of a ruler as only the uncertainty in one reading is included. You can also reduce uncertainty by measuring multiple instances, e.g. to find the time for 1 swing of a pendulum by measuring the time for 10 giving e.g. 6.2 ± 0.1 s, the time for 1 swing is 0.62 ± 0.01s (the uncertainty is also divided by 10).

Question 31

Repeated Data

Answer 31

For repeated data the uncertainty is half the range (largest - smallest value), show as mean + half the range

Question 32

Uncertainties SF

Answer 32

Uncertainties should be given to the same number of significant figures as the data.

Question 33

Adding / subtracting data

Answer 33

Add absolute uncertainties E.g. A thermometer with an uncertainty of ±0.5 K shows the temperature of water falling from 298±0.5 K to 273±0.5K, what is the difference in temperature? 298-273 = 25K 0.5+ 0.5 = 1K (add absolute uncertainties) difference = 25±1 K

Question 34

Multiplying / dividing data - Add percentage uncertainties

Answer 34

E.g. a force of 91±3 N is applied to a mass of 7±0.2 kg, what is the acceleration of the mass? uncertainty percentage uncertainty= Work out % uncertainties x 100 + 92 x 100 =3.3% + 2.9% add % uncertainties = 6.2% value x 100 So a = 13±6.2% ms-2 6.2% of 13 is 0.8 a= 13±0.8 ms-2

Question 35

Raising to a power

Answer 35

Multiply percentage uncertainty by power E.g. the radius of a circle is 5±0.3 cm, what is the percentage uncertainty in the area of the circle? Area = TT x 25 = 78.5 cm2 Area = TT/2 × 100 =6% % uncertainty in area = 6 x 2 (2 is the power from r2 ) % uncertainty in radius = 93 = 12% 78.5±12% cm2

Question 36

Applications and implications of science

Answer 36

An application of science is a use of scientific knowledge in order to carry out a specific action, an example of an application of science is developing a medical treatment, or carrying out further research based on prior knowledge. A radiation procedure, designed as a treatment for cancer, is an example of an application of science, and bears associated benefits: . Used as a treatment for cancer so it can potentially save lives. And risks: . Accidents may occur as it is a new technology, causing injury or even death. It is important to note that all applications of science will have their own associated benefits and risks. An implication of science is a direct or implied consequence of the knowledge of a particular concept. There are many different types of implications such as:

Question 37

Role of scientific community in validating new knowledge

Answer 37

Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered by the scientific community. However, these pieces of experimental evidence must first be published to allow them to be peer-reviewed by the community to become validated, and eventually accepted.