Activity is measured in becquerels (Bq) = 1 decay per second
Change in the number of radioactive nuclei in a given amount of time:
dN/dt = -λN
Half life = ln2/λ
Number of remaining atoms = N0e-λt
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Capacitors
C = Q/V Capacitance measured in Farads - 1 farad = 1C per V
I = Change in Q / Change in time
Uses for capacitors:
Flash photography
Defibrillators
Back up power supplies
the shorter the time taken for the capacitor to release the higher the current!
E = 1/2 x Q x V
E = 1/2 x CV2
Q = I x t
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Charging and Discharging
Factors affecting time of charge or discharge:
capacitance of capacitor, affects the amount of charge that can be transferred at a given voltage.
resistance of the circuit affects the current that can flow through the circuit.
The charge of a capacitor decreases exponentially.
Time constant τ = RC
Q = Q0e-1
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Simple harmonic motion
Frequency = 1/Time period
Displacement:
SHM starting from Maximum displacement - x = Acos(2πft)
SHM starting from the Midpoint - x = Asin(2πft)
Harmonic Oscillators:
F = kx (k is the spring constant)
T = 2π x *
E = 1/2 x kX2
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Free and forced vibrations
The total energy of a free oscillating mass on a spring:
Etotal = 1/2mv + 1/2k
a system can be forced to vibrate by a periodic external force
when the driving frequency approaches the natural frequency, the system gains more energy from the driving force and vibrates with a rapidly increasing amplitude
when this happens the system is resonating.
Damping happens when energy is lost to surroundings due to damping forces such as air. Amplitude reduced over time.
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