Expressing Quantities & SI Units Flashcards

All 12 cards in this deck

What are the SI base units, and their symbols, for length, mass, time, electric current, temperature and amount of substance?

metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol).

Which SI units (and symbols) are used for force, energy, power and pressure?

newton (N), joule (J), watt (W), pascal (Pa).

Which SI units (and symbols) are used for frequency, charge, potential difference, resistance and magnetic flux density?

hertz (Hz), coulomb (C), volt (V), ohm ($\Omega$), tesla (T).

Which unit, other than $\mathrm{m/s^2}$, can be used for gravitational field strength (the acceleration due to gravity $g$)?

$\mathrm{N/kg}$ — $\mathrm{N/kg}$ and $\mathrm{m/s^2}$ are equivalent units.

What do the prefixes giga, mega, kilo, centi, milli, micro and nano mean as powers of ten?

giga (G) $10^{9}$, mega (M) $10^{6}$, kilo (k) $10^{3}$, centi (c) $10^{-2}$, milli (m) $10^{-3}$, micro ($\mu$) $10^{-6}$, nano (n) $10^{-9}$.

True or false? A current of 200 mA is larger than a current of 0.5 A.

False. 200 mA $=$ 0.2 A, which is smaller than 0.5 A.

What are the steps to convert a quantity with a prefix into its base SI unit?

e.g. 4.5 kJ into J

1. Replace the prefix with its power of ten: k $= \times 10^{3}$

2. Multiply: $4.5 \times 10^{3} = 4500$

3. Answer: 4500 J

What are the steps to convert a time in hours into seconds?

e.g. 2 hours

1. Hours to minutes, $\times 60$: $2 \times 60 = 120$ min

2. Minutes to seconds, $\times 60$: $120 \times 60 = 7200$

3. Answer: 7200 s

What are the steps to convert a speed in km/h into m/s?

e.g. 72 km/h

1. Kilometres to metres, $\times 1000$: 72 000 m each hour

2. Hours to seconds, $\div 3600$: $72\,000 \div 3600 = 20$

3. Answer: 20 m/s

What are the steps to multiply two numbers in standard form and give the answer in standard form?

e.g. $(2 \times 10^{5}) \times (4 \times 10^{3})$

1. Multiply the front numbers: $2 \times 4 = 8$

2. Add the powers of ten: $5 + 3 = 8$

3. Answer: $8 \times 10^{8}$

To how many significant figures should the mean of repeat readings such as 0.74 s, 0.69 s and 0.81 s be given?

The same number of significant figures as the readings — 2 s.f., so 0.75 s.

True or false? A number written in standard form with a negative power of ten, such as $5 \times 10^{-3}$, is a negative number.

False. A negative power of ten means a small positive number (less than 1); $5 \times 10^{-3} = 0.005$.