Chapter 10 - Creating Models Flashcards Preview

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Flashcards in Chapter 10 - Creating Models Deck (40)
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1
Q

Why are some atoms radioactive?

A

If an atom has too many neutrons, not enough neutrons or too much energy it will be unstable.

Unstable atoms break down by releasing energy and/or particles to reach a stable form.

2
Q

What do we mean by ‘radioactive decay is a random process”

A

Random:

- Cannot tell when any ONE atom will decay or WHICH atom in a sample will decay next.

3
Q

How does a model help to explain decay?

A

You cannot predict the decay of an individual atom but with a large enough sample of unstable atoms, the overall behaviour shows a pattern.

Thus, you can predict how many atoms will decay in a given time.

4
Q

What is the activity of a sample?

A

Number of unstable atoms that decay each second.

5
Q

What does the decay constant represent?

A

The probability that any particular nucleus will decay in a given unit of time.

(measures how quickly an isotope decays)

Bigger the decay constant, more likely decay is and thus faster rate of decay

6
Q

Unit of decay constant

A

s^-1

7
Q

The activity of a sample is proportional to…

A

The size of the sample.

As atoms decay, sample size gets smaller and thus activity falls.

8
Q

Activity

A

Decay constant x N

A = λN

9
Q

What is activity measured in?

A

Becquerels:

1 Bq = 1 decay per second

10
Q

What is half life?

A

The average time it takes for the number of undecayed atoms to halve.

11
Q

Half life equation:

A

T = ln 2 / λ

12
Q

Decay equation

A

N = N0 e ^ - λt

13
Q

What are capacitors?

A

Things that store electrical charge and energy.

14
Q

What is capacitance?

A

A measure of the quantity of charge a capacitor can hold.

Defined as amount of charge stored per volt.

15
Q

How does a capacitor store charge?

A

When a power source pumps electrons from the positive plate to the negative plate.

16
Q

Capacitance

A

C = Q/V

in farads (F) where 1 farad = 1 CV^-1

17
Q

How can you find the energy stored by a capacitor?

A

From the area under a graph of p.d against charge stored.

18
Q

Energy of a capacitor

A

E = 1/2 QV

E = 1/2 CV^2

19
Q

What happens when a capacitor is connected to a battery?

A

Current flows around the circuit until the capacitor is fully charged then stops.

When the p.d across the capacitor is equal to the p.d across the battery, current falls to zero and capacitor is fully charged.

20
Q

Why does current reduce?

A

Initially the current is high but as charge builds up on the plates, electric repulsion makes it more difficult for electrons to be deposited.

21
Q

What happens when a charged capacitor is connected across a resistor?

A

The p.d drives a current through the circuit.

22
Q

What happens when the power source is removed from charging capacitor?

A

Capacitor discharges, acting as a battery sending charge as current through load.

23
Q

What are the 2 things that affect the time it takes for charge/discharge?

A
  1. Capacitance affects the amount of charge that can be transferred at a given voltage.
  2. Resistance affects th current.
24
Q

Charge equation/Voltage equation

A

Q = Q0 e ^ -t/RC

Same for voltage and current.

25
Q

What is the time constant.

A

The time constant RC is the time taken for the charge on a discharging capacitor to fall to 37% of the original charge.

Or for charge of charging capacitor to rise to 63% of original charge.

26
Q

What happens with a large capacitance and large resistance?

A

Takes longer to charge/discharge.

27
Q

What is simple harmonic motion?

A

An oscillation in which the acceleration of an object is directly proportional to its displacement from the midpoint (and is directed towards the midpoint)

Restoring force is proportional to displacement.

28
Q

Equations for displacement, velocity and acceleration

A

s = A sin wt

v = Aw cos wt

a = - Aw^2 sin wt
a = -w^2 s
29
Q

What are the two possible oscillation equations?

A

At maximum displacement at time 0,

s = A cos 2pi f t

At midpoint at time 0,

s = A sin 2pi f t

30
Q

What does it mean to be isochronous?

A

Pendulums and other oscillators are isochronous meaning that the time period is independent of the amplitude.

31
Q

Energy stored by stretching or compressing a spring:

A

E = 1/2 k x^2

32
Q

At t = 0

S =
V =
A =

A

S = A

V = Aw

A = Aw^2

33
Q

Time period of simple harmonic oscillator

A

T = 2π √(m/k)

34
Q

s’’ =

A
  • k/m x

since F = ma = ms’’

and F = -kx

35
Q

What is the natural frequency of a system?

A

Frequency it oscillates at with no driving force.

36
Q

Total energy of a freely oscillating mass on a spring

A

E = KE + PE

E = 1/2 mv^2 + 1/2 kx^2

37
Q

What is resonance?

A

When the driving frequency = natural frequency the system gains more and more energy from the driving force and thus vibrates with a rapidly increasing amplitude.

38
Q

What does damping do?

A

Reduces the amplitude of the oscillation over time as the system loses energy to its surroundings.

39
Q

Critical damping

A

Reduces the amplitude in the shortest possible time.

40
Q

Overdamping

A

Takes longer to return to equilibrium than a critically damped system.