# Chapter 10 - Models in Physics

• Created by: Helena
• Created on: 31-03-15 12:38
What is radioactive decay?
Unstable atoms breaking down by releasing energy and/or particles, until they reach a stable form.
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What is the activity of a sample? What is it's unit?
The number of unstable atoms that decay each second. Unit= becquerels (Bq) , 1 becquerel = 1 decay per second
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What is the decay constant?
The probability of a given nucleus decaying in a certain time (second). Unit, S^-1
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What is teh equation for activity?
Activity= decay constant * number of radioactive nuclei remaining.
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What is activity equivalent to graphically?
dN/dT, th gradient of N against time which is negative.
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What is the half-life of an isotope?
The average time it takes for the no. of undecayed atoms to half. Measured by time it takes for activity to half.
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What is the equation for half-life?
T1/2 = Ln2/ Decay constant
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What is capacitance?
The amount of energy stored per votl.
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Give some examples of things capacitors are used in.
Flash photography/ Defibrillators/ Back-up power supply.
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What is the equation for capacitance?
C=Q/V Capacitance= Charge/Potential difference
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What are the 2 equations for energy stored by the capacitor?
E=1/2QV E=1/2CV^2 E
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What is a dielectric material? What is it's use?
An insulating material. Keeps conducting plates form coming into contact, allows for smaller seperation to increase capacitance and reduce possibility of shorting by sparking.
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If you plot charge over time what will the graph look like and what will the gradient tell you?
Looks a bit like a rootX graph, the gradient tells you the current.
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What is capacitance measured in?
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How can you increase the capacitance?
Decrease the plate separation so electric field strength is increased and charge density increased so capacitance increased. Or increase the surface area which means more charge can accumulate on the plates. Choose a good dielectric material.
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How does the capacitor work?
Electrons flow onto plate connected to positive terminal of battery, negative charge build up. This repels electrons off plate connected to positive terminal- making plate positive. Equal but opposite charge buildup on the plates causing p.d. across.
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How does discharging a capacitor work?
Connect charges capacitor across resistor, p.d. drives current through circuit. Current flows opposite to charging current. Discharged when p.d. across plates and battery is zero.
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What type of graph shows the rate of discharge against time?
Exponential. Rate of discharge = dQ/dT= -Q/RC
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What is the time constant?
= RC , time taen for the charge on a discharging capacitor to fall to 37% of initial charge. Or to rise to 63%.
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What is simple harmonic motion?
An oscillation in which the acceleration of an object is directly proportional to it's displacement form the midpoint, and is directed towards the midpoint.
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What is the displacement in SHM?
The distance from the object to the midpoint.
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What does the restoring force do?
Makes object exchange PE and KE.
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When are the PE and Ke maximum?
KE max in middle. PE max at edges of oscillation.
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When plotted against time which two features are exactly 180 degrees out of phase?
Displacement and acceleration.
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What is the frequency and period of a SHM?
Frequency- no. of cycles per second. Period- time for complete cycle.
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Are frequency and period independent of amplitude in SHM?
Yes
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What is the SHM equation for acceleration?
a= -(2 pi f)^2x x= displacement
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What is teh SHM equation for displacement starting at max displacement and mid.
x=Acos(2(pi)ft) for max. x=Asin(2(Pi)ft) for mid.
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What is an isochronous oscillation?
Oscillation with the same period/frequency.
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What is the equation for the size of force exerted when pushed/pulled left/right of equilibrium?
F=KX K=springs constant(Nm-1) X= displacement(m)
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WHat type of energy does compressing or stretching a spring store?
Elastic potential energy
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What is a forced vibration?
A vibration caused by a external driving force
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What is resonance?
When the driving frequency= natural freequency
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What is damping?
When energy is lost to surroundings. Frictional forces- deliberate damping.
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How does damping affect resonance?
Light damping- Sharp resonance peak. Heavy damping- flatter response.
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## Other cards in this set

### Card 2

#### Front

What is the activity of a sample? What is it's unit?

#### Back

The number of unstable atoms that decay each second. Unit= becquerels (Bq) , 1 becquerel = 1 decay per second

### Card 3

#### Front

What is the decay constant?

### Card 4

#### Front

What is teh equation for activity?

### Card 5

#### Front

What is activity equivalent to graphically?