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MODULE 6
6.1 CAPACITORS
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Cards (51)
What is a capacitor?
An
electrical
component that stores
charge
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What is the purpose of the dielectric in a capacitor?
To prevent
charge
from traveling across the gap
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How is capacitance defined mathematically?
Capacitance
,
C
C
C
, is
C
=
C =
C
=
Q
V
\frac{Q}{V}
V
Q
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In what unit is capacitance measured?
Farads
, F
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What happens when a capacitor is connected to a DC power supply?
Current flows until potential difference equals
e.m.f
.
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What charges do the plates of a capacitor hold after connection to a power supply?
One plate holds charge +
Q
Q
Q
, the other -
Q
Q
Q
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What is the role of the dielectric in increasing capacitance?
It polarizes in the
electric field
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What is electrical permittivity?
It describes a
dielectric's
ability to
polarize
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Why are materials like air or vacuum poor dielectrics?
They do not
polarize
well
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What does Kirchhoff’s voltage law state?
The sum of
e.m.f.s
equals the sum of
potential differences
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How is the total capacitance of capacitors in series calculated?
Using
1
C
T
=
\frac{1}{C_T} =
C
T
1
=
1
C
1
+
\frac{1}{C_1} +
C
1
1
+
1
C
2
+
\frac{1}{C_2} +
C
2
1
+
…
\ldots
…
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What is the formula for combined capacitance in series?
C
T
=
C_T =
C
T
=
\left( \frac{1}{C_1} +
1
C
2
+
\frac{1}{C_2} +
C
2
1
+
\ldots \right)^{-1}
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How is the total capacitance of capacitors in parallel calculated?
latex>C_T = C_1 + C_2 + C_3 + \ldots</latex>
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What must be done to charge a capacitor?
Work must be done by the
power supply
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What does the area under the charge-voltage graph represent?
Work done
in charging the
capacitor
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What is the formula for energy stored in a capacitor?
W
=
W =
W
=
1
2
Q
V
\frac{1}{2} Q V
2
1
Q
V
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How can the energy stored in a capacitor also be expressed?
W
=
W =
W
=
1
2
V
2
C
\frac{1}{2} V^2 C
2
1
V
2
C
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What is the role of capacitors in camera flashes?
To store and
discharge
large energy quickly
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How do capacitors function in uninterrupted power supplies (UPS)?
They provide
backup
power
when
mains
fail
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What happens to AC current after passing through a full wave rectifier?
It flows in one
direction
but varies
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How do capacitors help maintain a constant current?
They store energy as
p.d.
rises and discharge as it falls
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What occurs when a capacitor is discharged?
Electrons
flow and dissipate energy as heat
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What determines the time constant of a discharging capacitor?
Capacitance
and resistance in the circuit
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How does resistance affect the current during discharging?
Lower resistance allows
higher
current flow
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What is the relationship between capacitance and charge stored?
Higher
capacitance means
larger
charge stored
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What does the symbol
∼
\sim
∼
indicate in the context of capacitance?
It means 'goes as' or
proportional
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Why is the relationship between current and charge not simple during discharging?
Current is not
constant
while discharging
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What is the relationship between resistance and current in a discharging circuit?
The
lower
the resistance, the
higher
the current
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How does current relate to charge on the plates in a capacitor?
Higher
current
leads to
faster
charge
drop
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What does capacitance measure in a capacitor?
Charge stored per unit
potential difference
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What is the formula for capacitance?
C
=
C =
C
=
Q
V
\frac{Q}{V}
V
Q
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What happens to the charge on a capacitor as it discharges?
The
charge
decreases
as
time
progresses
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What is the maximum potential difference across the plates before discharging?
V
0
=
V_0 =
V
0
=
Q
0
C
\frac{Q_0}{C}
C
Q
0
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What happens to the current as the charge stored on the capacitor decreases?
The
current
also
decreases
over
time
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What is the relationship between current and charge in a discharging capacitor?
I
=
I =
I
=
−
d
Q
d
t
-\frac{dQ}{dt}
−
d
t
d
Q
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Why is there a negative sign in the current equation for discharging capacitors?
Conventional current flows opposite to
electron flow
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What is the result of separating variables in the current equation?
It allows
integration
to find charge over
time
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What is the final equation for charge in a discharging capacitor?
Q
=
Q =
Q
=
Q
0
e
−
t
C
R
Q_0 e^{-\frac{t}{CR}}
Q
0
e
−
CR
t
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How are voltage and current related to charge in a capacitor?
Voltage and current are related by
V
=
V =
V
=
I
R
IR
I
R
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What is the equation for voltage in a discharging capacitor?
V
=
V =
V
=
V
0
e
−
t
C
R
V_0 e^{-\frac{t}{CR}}
V
0
e
−
CR
t
View source
See all 51 cards
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