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level: Uses of SI units and their prefixes

Questions and Answers List

level questions: Uses of SI units and their prefixes

Question	Answer
The SI unit for mass is the kilogram (kg).	Mass (m)
What is the SI unit for mass?	Kilogram (kg).
The SI unit for length is the metre (m).	Length (l)
What is the SI unit for length?	Metre (m).
The SI unit for time is the second (s).	Time (t)
What is the SI unit for time?	Second (s).
The SI unit for the amount of substance is the mole (mol).	Amount of Substance (n)
What is the SI unit for the amount of substance?	Mole (mol).
The SI unit for temperature is the kelvin (K).	Temperature (T)
What is the SI unit for temperature?	Kelvin (K).
The SI unit for electric current is the ampere (A).	Electric Current (I)
What is the SI unit for electric current?	Ampere (A).
The SI unit of force is derived from F = ma, where m is mass (kg) and a is acceleration (m/s²). Thus, the SI unit of force is kg·m·s⁻², also known as a Newton (N).	Force (F)
What is the SI unit of force derived from F = ma?	kg·m·s⁻², also known as Newton (N).
The SI unit for energy is derived from the formula E = ½ mv². The units for mass (m) are kg and for speed (v) are m·s⁻¹, so the unit for energy is kg·m²·s⁻².	Energy (E)
What is the SI unit of energy derived from E = ½ mv²?	kg·m²·s⁻².
The SI unit for charge is derived from Q = I·t, where I is current (A) and t is time (s). Thus, the SI unit for charge is A·s.	Charge (Q)
What is the SI unit of charge derived from Q = I·t?	A·s (ampere-seconds).
The SI unit of voltage is derived from V = E/Q, where E is energy and Q is charge. The unit for energy is kg·m²·s⁻², and charge is A·s. Thus, the SI unit for voltage is kg·m²·s⁻³·A⁻¹.	Voltage (V)
Below are the prefixes which could be added before any of the above SI units	Prefixes
Some examples using prefixes:	Examples of Prefixes
To convert mega electron volts (MeV) to electron volts (eV), multiply by 10^6.	Conversion of MeV to eV
How do you convert mega electron volts (MeV) to electron volts (eV)?	Multiply by 10^6.
To convert electron volts (eV) to joules (J), multiply by 1.6×10^-19.	Conversion of eV to Joules
How do you convert electron volts (eV) to joules (J)?	Multiply by 1.6×10^-19.
To convert 76 MeV to joules, first convert to eV by multiplying by 10^6 then to joules by multiplying by 1.6×10^-19. Result: 1.216 times 10^{-11} J.	Conversion Example (MeV to Joules)
How do you convert 76 MeV to joules?	First convert to eV by multiplying by 10^6 then to joules by multiplying by 1.6×10^-19. Result: 1.216 times 10^{-11} J.
To convert kilowatt hours (kWh) to joules (J), use the formula: 1 kWh = 1000 J/s × 3600 s = 3.6×10^6 J.	Conversion of kWh to Joules
How do you convert 1 kWh to joules?	Use the formula: 1 kWh = 1000 J/s × 3600 s = 3.6×10^6 J, or 3.6 MJ.
Orders of magnitude are powers of ten used to describe the size of an object and to compare sizes of different objects.	Orders of Magnitude
What are orders of magnitude used for?	They describe the size of an object and compare sizes of different objects.
The diameter of nuclei is typically around 10^−14 meters.	Diameter of Nuclei
What is the order of magnitude for the diameter of nuclei?	10^−14 metres
100 m is two orders of magnitude greater than 1 m.	Comparing Orders of Magnitude
How many orders of magnitude is 100 m greater than 1 m?	Two orders of magnitude.
To give a value to the nearest order of magnitude, calculate the value and express it as a power of ten.	Approximating Orders of Magnitude
How do you approximate a value to the nearest order of magnitude?	Calculate the value and express it as a power of ten.
To find the approximate area of a spherical object (like a hydrogen atom), use the formula A=πr^2	Estimating Area (Example)
How do you estimate the area of a spherical object to the nearest order of magnitude?	Use A=πr^2 and express the result as a power of ten.
For a hydrogen atom with a diameter of 1.06 x 10^-10 m, the area is 8.82 x 10^-21 m² = 1 x 10^-20	Example Calculation
For a hydrogen atom with a diameter of 1.06×10^−10m, what is the approximate area to the nearest order of magnitude?	10^-20m²
Estimation helps physicists approximate physical quantities for comparison or to check if calculated values are reasonable.	Importance of Estimation
Why is estimation important in physics?	It helps approximate values for comparison or to verify if calculated values are reasonable.