Define physical quantity .

A physical quantity consists of a numerical magnitude and a unit ; a letter alone, without a unit, is meaningless.

If v represents velocity, the unit would be .......... .

If v represents velocity, the unit would be m s -1 .

Name three different physical quantities that the letter V can represent.

Volume , potential and voltage .

True or False? If V represents voltage, its unit would be m 3 .

False. m 3 is the unit of volume ; if V represents voltage , the unit is instead V (volts).

Define SI base units .

SI base units are the independently defined units from which every other physical unit can be derived; this is the standard system of measurement used in almost every country.

Name the six SI base units required for this course.

mass — kilogram (kg) length — metre (m) time — second (s) electric current — ampere (A) temperature — kelvin (K) amount of substance — mole (mol)

True or False? All units used in physics are SI base units.

False. Most units are derived units , formed by combining the SI base units (e.g. the newton, joule and pascal).

What are derived units ?

Derived units are units formed by combining the SI base units, deduced from the defining equation of the physical quantity.

State the base units of the newton (N), the unit of force.

kg m s -2 (from force = mass × acceleration).

State the base units of the joule (J), the unit of energy.

kg m 2 s -2 (from energy = ½ × mass × velocity 2 ).

State the base units of the pascal (Pa), the unit of pressure.

kg m -1 s -2 (from pressure = force ÷ area).

True or False? The kilogram is an SI base unit.

True. The kilogram (kg) is one of the seven SI base units.

Define homogeneity of a physical equation.

An equation is homogeneous when the units on both sides of the equation are equal (checked using SI base units).

Describe how to check whether a physical equation is homogeneous.

Check the units on both sides of the equation; if they are equal, the equation is homogeneous; if they do not match, the equation needs to be adjusted.

True or False? An equation can be homogeneous even if the units on each side are different, as long as the numbers match.

False. Homogeneity depends on the units (not just the numbers) on both sides of the equation being equal.

Give an example of the range of values physical quantities can span, in terms of powers of ten.

The diameter of an atom is about 10 -10 m, whereas the width of a galaxy may be about 10 21 m — a difference of 31 powers of ten.

The prefix femto (f) is equal to .......... , although it is not required by the OCR specification.

The prefix femto (f) is equal to 10 -15 , although it is not required by the OCR specification.

Define powers of ten .

Powers of ten are numbers obtained by multiplying 10 by itself repeatedly (e.g. 10 2 , 10 3 ), used to express very large or very small physical quantities.

Define the convention for labelling a table heading .

A table heading is labelled with the quantity symbol , followed by a forward slash and the unit (e.g. I / A ); units should never appear in the body of the table.

Which variable is plotted on the x-axis of a graph, and which on the y-axis?

The independent variable is plotted on the x-axis; the dependent variable is plotted on the y-axis.

What proportion of the space provided should a plotted graph cover?

At least 75 % of the space provided.

A y-intercept must always be read from an axis that starts at .......... .

A y-intercept must always be read from an axis that starts at x = 0 .

State three requirements of a line of best fit on a graph.

Roughly equal points on either side of the line Should not be forced through the origin Must be a thin, clear line drawn with a straight edge or ruler

In a data table, where should any processed data (e.g. averages) be recorded?

In columns to the far right of the table.

What step sizes should be used to give a suitable scale on a graph axis?

Steps of 1, 2, 5 , or a multiple of 10 .

A LevelPhysicsOCRFlashcards2. Foundations in PhysicsPhysical Quantities & Units

Physical Quantities & Units (OCR A Level Physics): Flashcards

Exam code: H556

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Define physical quantity.

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Cards in this collection (25)

Define physical quantity.
A physical quantity consists of a numerical magnitude and a unit; a letter alone, without a unit, is meaningless.
If v represents velocity, the unit would be ...........
If v represents velocity, the unit would be m s^-1.
Name three different physical quantities that the letter V can represent.
Volume, potential and voltage.
True or False?
If V represents voltage, its unit would be m³.
False.
m³ is the unit of volume; if V represents voltage, the unit is instead V (volts).
Define SI base units.
SI base units are the independently defined units from which every other physical unit can be derived; this is the standard system of measurement used in almost every country.
Name the six SI base units required for this course.
- mass — kilogram (kg)
- length — metre (m)
- time — second (s)
- electric current — ampere (A)
- temperature — kelvin (K)
- amount of substance — mole (mol)
True or False?
All units used in physics are SI base units.
False.
Most units are derived units, formed by combining the SI base units (e.g. the newton, joule and pascal).
What are derived units?
Derived units are units formed by combining the SI base units, deduced from the defining equation of the physical quantity.
State the base units of the newton (N), the unit of force.
kg m s^-2 (from force = mass × acceleration).
State the base units of the joule (J), the unit of energy.
kg m² s^-2 (from energy = ½ × mass × velocity²).
State the base units of the pascal (Pa), the unit of pressure.
kg m^-1 s^-2 (from pressure = force ÷ area).
True or False?
The kilogram is an SI base unit.
True.
The kilogram (kg) is one of the seven SI base units.
Define homogeneity of a physical equation.
An equation is homogeneous when the units on both sides of the equation are equal (checked using SI base units).
Describe how to check whether a physical equation is homogeneous.
Check the units on both sides of the equation; if they are equal, the equation is homogeneous; if they do not match, the equation needs to be adjusted.
True or False?
An equation can be homogeneous even if the units on each side are different, as long as the numbers match.
False.
Homogeneity depends on the units (not just the numbers) on both sides of the equation being equal.
Give an example of the range of values physical quantities can span, in terms of powers of ten.
The diameter of an atom is about 10^-10 m, whereas the width of a galaxy may be about 10²¹ m — a difference of 31 powers of ten.
The prefix femto (f) is equal to .........., although it is not required by the OCR specification.
The prefix femto (f) is equal to 10^-15, although it is not required by the OCR specification.
Define powers of ten.
Powers of ten are numbers obtained by multiplying 10 by itself repeatedly (e.g. 10², 10³), used to express very large or very small physical quantities.
Define the convention for labelling a table heading.
A table heading is labelled with the quantity symbol, followed by a forward slash and the unit (e.g. I / A); units should never appear in the body of the table.
Which variable is plotted on the x-axis of a graph, and which on the y-axis?
The independent variable is plotted on the x-axis; the dependent variable is plotted on the y-axis.
What proportion of the space provided should a plotted graph cover?
At least 75 % of the space provided.
A y-intercept must always be read from an axis that starts at ...........
A y-intercept must always be read from an axis that starts at x = 0.
State three requirements of a line of best fit on a graph.
- Roughly equal points on either side of the line
- Should not be forced through the origin
- Must be a thin, clear line drawn with a straight edge or ruler
In a data table, where should any processed data (e.g. averages) be recorded?
In columns to the far right of the table.
What step sizes should be used to give a suitable scale on a graph axis?
Steps of 1, 2, 5, or a multiple of 10.

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