3B SCIENTIFIC PHYSICS 1017781 Manual De Instrucciones página 7

7. Experiments
7.1 Plotting of charging curve
• Set the voltage level selector to 0.5 V and
determine the charging time as specified un-
der 6.4.
•
To measure the time for the next value, turn
the selector switch up to the next level and
repeat each step of the procedure.
U / V
10
8
6
4
2
0
0 10 20
Fig. 2 Charging curve for built-in RC pair no. 3
7.2 Plotting of discharging curve
•
Set the voltage level selector to 9.5 V and
determine the discharging time as specified
under 6.5.
•
To measure the time for the next value, turn
the selector switch down to the next level and
repeat each step of the procedure.
U / V
10
8
6
4
2
0
0 10 20
Fig. 3 Discharging curve for built-in RC pair no. 3
30 40 50 60
t / s
30 40 50 60
t / s
7.3 Determining the values of the capacitors
and resistor being used
Theoretically the discharging time τ
and the charging time τ
both cases, the following applies:
τ = τ = = − ⋅
t
C DC 5%
If either R or C is known, then the other value can
be calculated from τ. It is possible to obtain
greater accuracy for τ by the following means:
•
Measure the discharge time τ
times and take the average of the results.
•
Measure the charging time τ
times and take the average of the results.
•
Take the average
average values for charging and discharging.
7.4 Determining the capacitance C of an ex-
ternal capacitor
•
Plug in a known resistor R
kΩ along with the capacitor for which the ca-
pacitance C
70
e
•
Set the selector switch to EXTERN.
•
Measure the time t
•
Calculate the capacitance of the external
capacitor:
C
7.5 Determining the capacitance C
internal capacitor
•
Set the selector switch to INTERN 3.
• Measure the time τ
•
Plug in an external capacitor C
• Measure the time τ
The following is now true:
τ = ⋅ ⋅ τ = ⋅
3 C R ,
1 i 3
τ
=
2
Therefore:
τ
1
τ
C
=
or i 1
τ − τ
C
e 2 1
7.6 Determining the values of the internal
resistors
70
•
Set the selector switch to INTERN 1, IN-
TERN 2 or INTERN 3.
•
Measure the time t
•
Calculate the resistance of the respective
internal resistor:
3
DC
for 9.5 V are identical. In
C
( )
⋅ ≈ ⋅ ⋅
ln 20 3
C R C R
for 0.5 V three
DC
for 9.5 V three
C
1
(
= τ + τ
t
5% C
2
of no less than 10
e
is to be determined
as specified under 7.3.
5%
t
=
5%
e
⋅
3 R
e
as specified under 7.3.
1
.
e
as specified under 7.3.
2
( )
+ ⋅
3 C
C R
2 i e 3
+
C C C
= +
i e e
1
C C
i i
as specified under 7.3.
5%
t
= .
5%
R
i
⋅
3
C
i
for 0.5 V
.
)
of the
DC
of the
i