Need help with Q 27 please.
Transcribed Image Text: 30.23 Sodium ions (Na+) are flowing
through a cylindrical ion channel which
has a diameter of 0.85 µm and is 5 μm
long. There is a potential difference of
225 mV between the ends of the chan-
nel. The sodium ions have a drift velocity
through the channel of 0.015 m s-¹ and
in a period of 1 ms a total of 15 x 106 ions
exit the channel.
(a)
What total charge exits the channel
in a time period of 1 ms?
(b) What is the current in the ion chan-
nel?
(c) What is the 'resistance' of the chan-
nel to the flow of sodium ions?
(d) What is the number density, n, of
ions in the channel?
(e) How many sodium ions are in the
channel at any one time?
30.24 Given that the potential is +18 V at
the point shown, what is the electrical po-
tential at the points A, B, C, and D in the
circuit shown in Figure 30.28?
3 Ω
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+18 V
A
D
202
¾
252
B
Figure 30.28 A circuit with 5 resistors and a single bat-
tery.
30.25 A simple circuit is constructed in
which a 1 Q resistor is connected across
a 1 V battery and so draws a 1 A current.
What is the current drawn from the bat-
tery if:
(a)
an extra 1 2 resistor is connected in
series with the existing one?
(b) four extra 12 resistors are con-
nected in series with the existing
one?
30.26 A simple circuit is constructed in
which a 1 9 resistor is connected across
a 1 V battery and so draws a 1 A current.
What is the current drawn from the bat- (f)
tery if:
(a)
(b)
30.27 Circuit A shown in Figure 30.29
consists of a single light bulb (R = 288 22)
and a 12 V battery.
(a)
(b)
an extra 1 2 resistor is connected in (g) What is the total power supplied by
parallel with the existing one?
the battery?
four extra 1 resistors are con-
nected parallel with the existing
one?
(d)
12 V
(e)
12 V
12 V
Circuit A
Circuit B
288 Ω
288 Ω
288 Ω
Figure 30.29 Three circuits showing different arrange-
ments of light bulbs.
288 Ω
Circuit C
288 Ω
What current is drawn from the bat-
tery?
An identical light bulb is now added
to Circuit A in series with the first (see Cir-
cuit B in Figure 30.29).
(c)
What is the power dissipated in the
light bulb?
What is the current drawn from the
battery in this case?
What is the current passing through
each light bulb?
An identical light bulb is added to Circuit
A in parallel with the first (see Circuit C in
Figure 30.29).
(h)
(i)
(j)
(k)
(1)
What is the power dissipated in
each light bulb?
(d)
What is the current drawn from the
battery in this case?
(e)
What is the current passing through
each light bulb?
(f)
What is the potential difference
across each light bulb?
30.28 Five resistors are connected to a
24 V resistor as shown in Figure 30.30.
(a) What is the total resistance of the
circuit?
What is the power dissipated in
each light bulb?
(b) How much current flows from the
battery?
What is the total power supplied by
the battery?
(c) How much power is supplied by the
battery?
What is the potential difference
across each resistor?
What is the current through each re-
sistor?
What is the power dissipated in
each resistor?
8 Ω
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4Ω
6Ω
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3 Ω
What is the potential difference Figure 30.30 A circuit with 5 resistors in both series and
across each light bulb?
parallel.