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(A-Level) Physics > Module 2: C2 - Foundations Of Physics > Flashcards

Module 2: C2 - Foundations Of Physics Flashcards

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1
Q

What is a Physical Quantity

A

A physical quantity is a measurement of something.

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2
Q

What are SI units?

A

These are the standard units used by the international scientific community.

For example, the metre is the standard unit for a physical quantity of length.

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3
Q

What are the 7 SI base units

Quantity, Unit, (Unit Symbol)

A
  • Mass, Kilogram (kg)
  • Length, Metre (m)
  • Time, Second (s)
  • Temperature, Kelvin (K)
  • Electrical Current, Ampere (A)
  • Amount of substance, Mole (mol)
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4
Q

Derived Unit for Acceleration

A

Meter per second squared

ms^-2
(m/s^2)

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5
Q

Derived Unit for Force

A

Force has the standard SI unit: newton, N

Since force can be calculated by multiplying mass and acceleration (𝐹 = 𝑚𝑎), this means that a newton is equivalent to

kg ms^-2

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6
Q

Derived Unit for Frequency

A

Unit: hertz (hz)

f = 1/t
= 1/s, or s^-1

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7
Q

Derived Unit for Pressure

A

Unit: Pa

P = F/A

= kg m^-1s^-2

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8
Q

Derived Unit for Energy

A

Unit: J

E = Fd

=Ns

= kg m^2s^-2

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9
Q

Derived Unit for Power

A

Unit: W

P = E/T

= kg m^2s^-2/s

= kg m^2 s^-3

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10
Q

Derived Unit for Electric Charge

A

Unit: C

Q = It
= As

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11
Q

Derived Unit for Potential Difference

A

Unit: V

E = QV
V = E/Q
= kg m^2 s^-2 / As

= kg m^2 s^-3 A^-1

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12
Q

Derived Unit for Electrical Resistance

A

Unit: Ω

kg m^2 s^-3 A^-2

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13
Q

What are the scientific units for standard form numbers ranging from (x^-12 to x^12)

A

terra (T) x 10^12
giga (G) x 10^9
mega (M) x 10^6
kilo (k) x 10^3

milli (m) x 10^-3
micro (µ) x 10^-6
nano (n) x 10^-9
pico (p) x 10^-12

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14
Q

What is Wein’s displacement constant

A

𝑏 = 2.898 x 10^-3 m K

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15
Q

SI Units for:

  • Charge
  • Distance
  • Current
  • Potential Difference
  • Energy
  • Force
  • Power
  • Speed
  • Acceleration
  • Momentum
  • Resistance
A

Charge - C (Q)
Distance - m (d)
Current - A (I)
Potential Difference - V (V)
Energy - J (E)
Force - N (F)
Power - W (P)
Speed - m/s (s)
Acceleration - m/s^2 (a)
Momentum - kg m/s (p)
Resistance: Ω (R)

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16
Q

What is Homogeneity (What makes an equation homogeneous?)

A

In any equation, every term has to have the same SI base units. If this is true, the equation is homogeneous.

Every real equation has to be homogeneous.

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17
Q

How is the equation ‘F =ma’ homogeneous

A

The left side has the unit: N

The right side has the unit: kg m s^-2

They are the same SI base units, as N = kg m s^-2

Therefore it is homogeneous and valid.

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18
Q

How is the equation ‘v = u + at’ homogeneous

A

There are 3 germs in this equation:

  • v has the SI unit of ms^-1
  • u has the SI base unit of ms^-1
  • at has the SI base unit of a x t which ms^-2 x s which is the same as m s^-1

All three terms have the same SI base units and so the equation is homogeneous and therefore valid.

19
Q

Homogeneous or not.

The momentum, p, of an object, measured in kg m s^-1 is given by

p = mv

where m is the objects mass and v is it’s velocity

A

p = mv

kg ms^-1 = kg x ms^-1

kg ms^-1 = kg ms^-1

The equation is homogeneous, as it involves the same SI units on both sides.

20
Q

What conclusion can reach if an equation is/isn’t homogeneous?

A

If an equation isn’t homogeneous, then it’s definitely wrong, but if it is homogeneous, then it could be correct.

21
Q

Definition of an Astronomical Unit (AU)

A

An Astronomical Unit is the mean distance of the Earth from the Sun as defined in 1938. The current value is about 1.50x10^8km, or 9.30x10^7 miles.

22
Q

Definition of a Light Year

A

A Light Year is the distance travelled by light in a vacuum in one tropical year, that is 9.46x10^12km or 5.88x10^12 miles.

23
Q

Definition of a Parsec (AU)

A

A Parsec is the distance at which an angle of one second of an arc will represent the distance of the Earth from the Sun, that is 2.06x10^5 astronomical units, 3.2616 light years or 3.09x10^13km (1.92x10^13 mile).

24
Q

What are Scalar quantities

A

A scalar quantity has magnitude (size), but no direction.

25
Q

What are Vector quantities

A

Vector quantities have a magnitude (size), and a direction.

26
Q

How can scalar quantities be added and subtracted

A

Scalar quantities can be added together or subtracted from one another in the usual way.

They must have the same units when you add or subtract them.

27
Q

How are scalar quantities multiplied and divided

A

Scalar quantities can also be multiplied together or divided by one another. However, in this case, the units can be the same or different , unlike adding and subtracting.

28
Q

Example Question:

A balloon is inflated with 6.1x10^-3m^3 of helium. It’s mass increases by 0.98g. Calculate the density of helium.

A

Step 1:
The equation for density is:
Density = Mass / Volume

Step 2:
Consider the units of the equation.
You are dividing together two scalar quantities. The SI base unit for mass is the kg. Volume has the unit m^3. The mass must be converted into kg before substitution; mass = 9.8 x 10^-4 kg.

Step 3:
Substitute the values into the equation and calculate the density.

Density = 9.8 x 10^-4 / 6.1 x10^3 = 0.16 kgm^-3

29
Q

Difference between distance and displacement

A

Distance and displacement are both measured in m, but distance is a scalar quantity and displacement is a vector quantity.

30
Q

How are Vector Quantities visually represented

A

A vector quantity is represented by a line with a single arrowhead.

  • The length of the line represents the magnitude of the vector, drawn to scale
  • The direction in which the arrowhead points represents the direction of the vector.
31
Q

How do you work out the resultant vector for Parallel Vectors?

A

Where two vectors are parallel (they act in the same line and direction), you just add them together to find the resultant vector.

The direction of the resultant is the same as the individual vectors but it’s magnitude is greater. For example, if two forces of 3.0N and 4.0N act in the same direction on an object, the resultant force is 7.0N.

32
Q

How do you work out the resultant vector for Antiparallel Vectors?

A

Where two vectors are antiparallel (they act in the same line but in opposite directions), you call one direction positive and the opposite direction negative (it does not matter which), and then add the vectors together to find the resultant.

The magnitude and direction of the resultant will depend on the magnitude of the two vectors.

33
Q

Worked Example:

Two forces act in the opposite directions on an object.

A force of 3N pulls towards the left, and a force of 4N pushes towards the right.

Calculate the magnitude and direction of the resultant force.

A

Step 1:

Assign the positive and negative values to the vectors.
Assume that the positive direction is towards the right, so the two forces are -3.0N and +4.0N.

Step 2:

Calculate the resultant force.
Resultant = -3.0 + 4.0 = +1.0N towards the right.

34
Q

What two methods can be used to find a Resultant Vector

A

The resultant vector can be found either by calculation or by scale drawing of a vector triangle.

35
Q

How can you find the Resultant Vector by scale drawing of a vector triangle (Method)

A
  1. Draw a line to represent the first vector.
  2. Draw a line to represent the second vector, starting from the end of the first vector.
  3. To find the resultant vector, join the start to the finish. You have created a triangle.

(This method can be used to determine the resultant vector for any two vectors - displacements, velocities, accelerations, and so on. The angle between the vectors doesn’t have to be 90°, any triangle works)

36
Q

How can you find the Resultant Vector by Calculation

A

If the angle is 90°, you can simply use Pythagoras theorem (a^2 = b^2 + c^2) to work out the length of the hypotenuse.

If the angle is not 90°, you could use the Sine Rule, a/SinA = b/SinB = c/SinC
or
You could use the Cosine Rule, a^2 = b^2 + c^2 - 2bc cos A

37
Q

How can you resolve a vector into two components

A

It can be done using a scale drawing, but more often vectors are resolved using calculation.

To resolve a force, F into the x and y direction, the two components of the force are:

  • Fx = F cos(Θ)
  • Fy = F sin (Θ)

Where Θ is the angle made with the x direction. These equations can be used with any vector in the place of x.

38
Q

Example Question:

At an airport, a horizontal wind is blowing 15m^-1 at an angle of 60° north of east. Calculate the component of the wind velocity in the north and east direction.

A

Step 1: Select the equations for resolving vectors.

  • Vx = cos (Θ)
  • Vy = sin (Θ)

Step 2: Substitute the values into the equations and calculate the components.

  • Velocity component due east = vx= 15 x cos(60) = 7.5ms^-1
  • Velocity component due north = vy = 15 x sin(60) = 13ms^-1

( v^2 = vx^2 + vy^2 = 7.5^2 + 13^2 = 56.25 + 169
v = 15ms^-1)

39
Q

Example Question:

A freely falling object has vertical acceleration of 9.81ms^-2. The object is placed on a smooth ramp that makes an angle of 30° to the horizontal. Calculate the component of the acceleration a down the ramp.

A

Step 1: Select the equation
Acceleration component down the ramp = a cos Θ where Θ is the angle a makes to the slope.

Step 2: Substitute the values into the equations and calculate the component.
Component = 9.81 x sin(30) = 4.91ms^-2

40
Q

What are the 3 Techniques used to Add Perpendicular Vectors

A
  • Scale Diagram
  • Calculations using Cosine and Sine rules
  • Calculations using vector resolution
41
Q

How to add Non-Perpendicular Vectors by using a Scale Diagram

A

Choose an appropriate scale for the drawing of your vector triangle.

Carefully measure the length of the resultant vector (e.g 7.0cm). If 1.0cm represented 1.0N in the diagram, the resultant force would equal 7.0N.

42
Q

How to add Non-Perpendicular Vectors using Calculations (with cosine and sine rules)

A

You can use the cosine rule (a^2 = b^2 + c^2 - 2bc cos Θ) to determine the magnitude of the resultant force.

The angle Θ can be found using the sine rule (a/sinA = b/sinB

43
Q

How to add Non-Perpendicular Vectors using Calculations (using vector resolution)

A

This technique relies on choosing convenient perpendicular axes. One of the vectors is resolved along each axis so that the magnitude of the resultant vector can be determined using Pythagoras’ theorem.

44
Q

How do you Subtract Vectors

A

Two vectors are represented by X and Y. To subtract Y from X, you simply reverse the direction of Y and then add this new vector to X.

(A-Level) Physics (27 decks)

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