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Physics > 10-Modelling decay > Flashcards

10-Modelling decay Flashcards

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1
Q

What is radioactive decay?

A

That the nuclei of some atoms are unstable and break down

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2
Q

What 3 types of particles do nuclei emit when they become unstable and break down?

A

Alpha, beta and gamma particles

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3
Q

What are alpha particles?

A

Helium nuclei

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4
Q

What are beta particles?

A

Fast moving electrons

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5
Q

What are gamma rays?

A

High energy photons

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6
Q

What is the activity of a source?

A

The number of nuclei decaying per second

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7
Q

What is the unit of activity?

A

The Becquerel, Bq

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8
Q

What is 1 Bq equivalent to?

A

1 Bq = 1 decay/second

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9
Q

What is the half life of a radioactive source?

A

The time required for the number of nuclei in a sample to fall to half the original value

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10
Q

What happens to the activity of a sample after 2 half lifes?

A

It decreases by a factor of 4

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11
Q

Is the process of radioactive decay random?

A

Yes, as a particle has a given probability of being emitted from a nucleus in a given time

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12
Q

What is similar between radioactive decay and flipping a coin?

A
  • The fall of an individual coin is random in the same way a decaying necleus is random
  • The outcome of many coins flipped is predictable, in the same way the decay of a large number of nuclei is predictable
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13
Q

What is the decay constant?

A

The probability that a nucleus will decay during a time interval of 1s

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14
Q

What is the unit of the decay constant?

A

s-1

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15
Q

What is the equation of the activity of a source?

A

Activity = probabilty of nucleus decaying in 1 second X number of nuclei present

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16
Q

What does the number, change in N equal?

A

Change in N = -decay constant X number of nuclei present X change in time interval

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17
Q

What does the change in nuclei / change in time interval equal?

A

-decay constant X total nuclei present

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18
Q

What is the activity proportional to?

A

The number of nuclei remaining

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19
Q

What is an example of exponential change?

A

When the rate of change of a quantity is proporitional to the value of the quantity

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20
Q

Why reduce the time intervals when making an iterative model of decay?

A

With larger time intervals, it suggests that the rate of decay is constant during the large time interval

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21
Q

What is the solution to the equation dN / dT?

A

N = N0 X e^-decay constant X time

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22
Q

As activity is proportional to the number of nuclei present, what equation can we deduce?

A

A = A0 X e^-decay constant X time

23
Q

What equation represents half life, decay constant and ln2?

A

Half life = ln2 / decay constant

24
Q

What is the gradient of a natural log of the activity against time graph?

A

-decay constant

25
Q

What is the equation of the line of natural log A against time?

A

ln A = lnA0 -decay constant X time

26
Q

How can the exponential decay of a radioactive source be modelled?

A

Using a simple iterative process

27
Q

What do capacitors store?

A

Capacitors store charge

28
Q

What is the basic design of a capacitor?

A

A pair of electrical conductors seperated by a thin layer of insulin

29
Q

Nowadays, what are capacitors made up of?

A

Sheets of metal foil with an insulating layer between them

30
Q

What happens when a potential difference is applied across the conductor plates?

A

Negative charge flows from the negative terminal of the cell to one plate, making it negative. An equal positive charge flows from the other plate to the cell through the positive terminal, making that plate positive

31
Q

What does the process of charge separation do?

A

It charges the capacitor

32
Q

What is the capacitance?

A

The charge separated per volt

33
Q

What is the equation of the capacitance?

A

C = Q / V

34
Q

What is the unit of capacitance?

A

The Farad

35
Q

What does the gradient of charge against potential difference give?

A

The capacitance

36
Q

What happens when the capacitor discharges?

A

Negative charge flows from the negative plate of the capacitor to the positive plate

37
Q

When a charge moves through a potential difference, what does the energy transferred equal?

A

QV

38
Q

When a capacitor is charged to a potential difference, what is the energy stored?

A

1/2 QV

39
Q

As Q=CV what does the energy equal?

A

1/2 CV^2

40
Q

What is the potential difference across a capacitor proportional to?

A

The charge on the capacitor

41
Q

What is the current through the resistor proportional to?

A

The potential difference across the resistor

42
Q

What does the charge leaving the capcitor in t seconds equal in terms of current?

A

Change in charge = - current X time period

43
Q

What does the charge leaving the capcitor in t seconds equal in terms of voltage and resistance?

A

Change in charge = - Voltage/resistance X time period

44
Q

What does the charge leaving the capcitor in t seconds equal in terms of charge, resistance and charge?

A

Change in charge = -Q/RC X time period

45
Q

What differential equation can you get for charge?

A

Q = Q0 C e^-t/RC

46
Q

What is Q0?

A

The charge at the beginning of the discharge

47
Q

As the potential difference across a capacitor is proportional to the charge on its plates, what equation can you obtain?

A

V = V0 X e^-t/RC

48
Q

As the current in the circuit is proportional to the potenital difference across the resistor, what equation can you obtain?

A

I = I0 X e^-t/RC

49
Q

What is the time constant?

A

RC

50
Q

What is the time constants units?

A

seconds

51
Q

What does t / RC equal?

A

1

52
Q

After RC seconds, what has the charge on the capacitor been reduced by?

A

1/e of its original value

53
Q

In terms of RC, what is the time taken for the charge to half?

A

0.693RC seconds

54
Q

Why is a charge against time graph for a capacitor shaped as it is?

A

Initially the current is high and the electrons start to build on the capacitor plate. As this happens the rate of flow of the electrons decreases as it becomes more difficult to add electrons to the plate due to electrostatic repulsion. Eventually the current stops flowing when the voltage across the capacitor equals the voltage across the power supply.

Physics (22 decks)

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