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Physics Unit 2
Capacitors
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Katie Lowry
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Cards (57)
What is the simplest arrangement of a capacitor?
Two
parallel
metal plates separated by an
insulator
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What materials typically make up the metal plates and insulator of a capacitor?
Thin
metal foil
and
plastic
or
waxed paper
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What is the primary function of a capacitor?
To store energy in an
electric field
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What does charging a capacitor involve?
Building
electric charges
of equal magnitude but
opposite polarity
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How is capacitance defined mathematically?
Capacitance is
charge
stored per
volt
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What is the formula for capacitance?
C
=
Q
/
V
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What does the symbol 'C' represent in the formula C = Q/V?
Capacitance
measured in
Farads
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What is the unit of capacitance?
Farads (F)
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Why are microfarads (μF) and picofarads (pF) more commonly used than Farads?
Because
Farads
is a very
large
unit
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What happens to the potential difference (pd) when electric charge is stored on the plates of a capacitor?
The pd between the plates rises
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What is the relationship between capacitance and charge in parallel capacitors?
The
pd
across each capacitor is the same
Total charge is the sum of
individual charges
Total capacitance is the sum of individual capacitances:
CT
=
C₁
+
C₂
+
C₃
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What is the relationship between capacitance and charge in series capacitors?
The charge on each capacitor is the same
The
total potential difference
is the sum of
individual voltages
: V = V₁ + V₂ + V₃
Total capacitance is given by: 1/
CT
= 1/
C₁
+ 1/
C₂
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How is the energy stored in a charged capacitor calculated?
Energy
is calculated as
W
=
QV
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What does the term 'discharging' refer to in capacitors?
Releasing
stored
energy
from the
capacitor
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What is the time constant in a capacitor circuit?
Time taken for voltage/current to fall to
37%
of initial value
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How is the time constant calculated?
It is the product of
capacitance
and
resistance
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What is the formula for the discharging current of a capacitor?
I =
I₀
e<sup>-t/
τ
</sup>
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What does the symbol 'e' represent in the discharging current formula?
The
exponential constant
, approximately
2.718
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How does the voltage across a capacitor change during discharging?
Voltage decreases
exponentially
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What is the formula for the charge stored in a capacitor during discharging?
Q =
Q₀
e<sup>-t/
τ
</sup>
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How can the initial voltage (V₀) of a capacitor be determined?
By using the
emf
of the battery or power supply
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How can the initial charge (Q₀) of a capacitor be calculated?
Q₀ =
CV₀
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How can the initial current (I₀) of a capacitor be calculated?
I₀ =
V₀
/
R
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What are the applications of capacitors in medical and photography fields?
Defibrillators
:
Deliver controlled shocks to restore heart rhythm
Store electric charge in an
electric field
Camera flashes:
Store energy
to produce
intense light
Discharge energy quickly through flash bulb
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What happens when a capacitor is fully charged?
It
discharges
through a
resistor
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How does the charging process of a capacitor occur?
Electrons flow onto one
plate
, repelling
electrons
from the other
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What role does a resistor play in the discharging of a capacitor?
It
slows
the
rate
of
discharge
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What is the effect of resistance on the current during discharging?
Current
decreases
over
time
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How does the voltage across a capacitor behave during charging?
It gradually increases until
fully charged
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What is the significance of the 37% value in capacitor circuits?
It represents the
time constant
for voltage/current decay
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What is the formula for calculating the time constant (τ) in RC circuits?
τ =
RC
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How can the time constant be measured in a circuit?
By plotting
ln(I)
against time
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What does the slope of the line in the ln(I) vs. time plot represent?
The negative reciprocal of the
time constant
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What is the relationship between the charge flow and the electric current in a capacitor?
Charge
flow
constitutes
an
electric current
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What happens to the voltage across a resistor when a capacitor discharges?
It follows the current curve due to
Ohm's law
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How does the initial charge affect the charging process of a capacitor?
It determines the amount of charge
transferred
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What is the role of the power supply in charging a capacitor?
It provides the voltage needed for charging
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What happens to the charge on the plates of a capacitor when it is fully charged?
The charge remains until
discharged
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How does the resistance in a circuit affect the time constant?
Higher
resistance
increases
the time constant
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What is the effect of capacitance on the charging time of a capacitor?
Larger
capacitance results in
longer
charging time
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