Skills - Units and Measurements

Question 1

What is scientific notation?

Answer 1

Standard form, used when numbers are very large or very small.

Question 2

What do significant figures do?

Answer 2

Gives an idea of the accuracy of the data collected, or the precision of the instrument used to make the measurements.

Question 3

What is the significant figures rule about leading zeros?

Answer 3

They do not count as significant. E.g, 0.00032 has 2sf.

Question 4

What is the significant figures rule about trailing zeros after a decimal point?

Answer 4

They do not count as significant. E.g, 0.0003200 has 2sf.

Question 5

What is the significant figures rule about trailing zeros without a decimal point?

Answer 5

They may or may not be significant. E.g, 500 can be 1sf (most likely), 2sf or 3sf. You will not be penalised for this as AQA accepts all of them as viable answers.

Question 6

What is the significant figures rule about calculations?

Answer 6

When carrying out calculations with quantities that have different sf, the answer of the calculation must be given to the same number of sf as the number with the lowest sf, because you cannot gain precision. Constants/numbers with no units do not apply to this rule. E.g, in the calculation 2π r, the r value would be the only contributing factor to the sf decision.

Question 7

What are base units?

Answer 7

A basic set of quantities and their units on which all other derived units can be made. These form the International System of Units (SI units).

Question 8

What are the SI units?(6)

Answer 8

• Length - metre - m
• Mass - kilogram - kg
• Time - second - s
• Electric Current - ampere - A
• Temperature - kelvin - K
• Amount of substance - mole - mol

Question 9

What are derived units?

Answer 9

A combination of two or more base units.

Question 10

What are the 9 main prefixes and there conversion factors?

Answer 10

• Tera - 10 (12)
• Giga - 10 (9)
• Mega - 10 (6)
• Kilo - 10 (3)
• BASE UNIT
• Centi - 10 (-2)
• Milli - 10 (-3)
• Micro - 10 (-6)
• Nano - 10 (-9)
• Pico - 10 (-12)

Question 11

How do you convert prefixes from the top to the bottom of the table?

Answer 11

The power stays as a positive number as the number gets bigger. You must add the power to get to the required prefix, or get to the base unit, then the required prefix. E.g, 6 km would become 6 x 10 (6) mm, as the conversion factors are -3 and 3.

Question 12

How do you convert prefixes from the bottom to the top of the table?

Answer 12

The power stays as a negative number as the number gets smaller. You must subtract the power to get to the required prefix, or get to the base unit, then the required prefix. E.g, 8 mm would become 8 x 10 (-6) km, as the conversion factors are -3 and 3.

Question 13

What is the rule for converting areas?

Answer 13

Convert normally, but put conversion to power of 2/square it => use brackets.

Question 14

What is the rule for converting volumes?

Answer 14

Convert normally, but put conversion to power of 3/cube it => use brackets.

Question 15

How do you convert combined units, such as km/h to m/s?

Answer 15

Convert the numerator to the correct unit, then convert the denominator to the correct unit then combine them. It’s best to do this by using fractions because it makes it easier to visualise.

Question 16

How can you avoid parallax error?

Answer 16

Read from directly above the object being measured + put ruler on/next to object.

Question 17

How can you improve accuracy?

Answer 17

Take multiple readings and find averages.

Question 18

What should the number of dp quoted be consistent with?

Answer 18

The accuracy of the device being used to measure => you can’t gain/lose accuracy.

Question 19

How can small thicknesses be measured?

Answer 19

By stacking copies of the item until there are enough to be measured, and dividing by how many there are to find the thickness of one copy of the item.

Question 20

How can you determine the diameter of a circular object?

Answer 20

Place two blocks at either end of the object and place the ruler so that it is at right angles to the blocks.

Question 21

How can you measure small radii?

Answer 21

Measure more than 1 of the object and divide by how many there are.

Question 22

What are the 3 requirements for a table?

Answer 22

• It must have a header stating the quantity + units with a separator (e.g, Length/m).
• The main body must only contain measurements to correct precision.
• No units or calculations should be in the body of the table.

Question 23

How is the vernier calliper scale used?

Answer 23

The main scale states what cm the object is to 0.0 cm. The vernier calliper tells you the 0.00 cm, by which line matches up with to on the main scale. For example for 3.47 cm, the seventh line on the vernier calliper scale would match up perfectly with the main scale.

Question 24

How do you correct for a zero error?

Answer 24

Adding/subtracting the necessary measurements. For example with a zero error of + 0.04cm, you would minus 0.04cm from all your results as they are 0.04cm too big, and vice versa for minus zero errors.

Question 25

How is the micrometer used?

Answer 25

Have a main scale on the top which is measured in mm. The bottom of the main scale is measured in 0.5mm. The vernier calliper scale is used to measure to the 0.01mm. Whichever number of the vernier calliper scale (which is round and on the end) matches up with the main scale is the correct 0.01mm. You can then add this value to the measurement taken from the main scale.

Question 26

How can accurate measurements of short-time periods be made using a stopwatch?

Answer 26

Measure more than one ‘period’ and divide the time by how many ‘periods’ you measured.

Question 27

How can time measures be further improved?(3)

Answer 27

Using;
* Light gates
* Motion sensors
* Mechanically triggered switches that are connected to an electronic timing device/computer

Question 28

How can masses of very small objects be found?

Answer 28

By finding the mass of multiple of the same object, and dividing the total mass by how many there are.

Question 29

How can masses of liquids be found?

Answer 29

By measuring the mass of the liquid and its container, and subtracting the mass of the container.Could also zero the scale with the container on it, and then add the liquid whilst the container is still on the zeroed scale.

Question 30

How do you find the volume of a cube/box?

Answer 30

volume = width x length x height

Question 31

How do you find the volume of a sphere?

Answer 31

volume = 4/3 x π x radius (2)

Question 32

How do you find the volume of a cylinder?

Answer 32

volume = π x radius (2) x height

Question 33

How can you find the volume of irregular shaped objects?

Answer 33

• Irregular shaped objects can be immersed in a partially filled measuring cylinder. The rise in level on the volume gives the volume of the solid.
• A displacement can may also be used to measure the volume of an irregular shaped object, by collecting the water that comes out the spout in a measuring cylinder. This collected volume of water is equivalent to the volume of the object.

Question 34

How do you measure density and what are the units used?

Answer 34

• Density = Mass/Volume
• Units;kg/m (3)or g/cm (3)