The flowchart below shows the components that make up an electronic sensor. sensing device
What are the names of the missing components? 2
3
A thermistor is an example of a sensing device. a b
ketc ketch h the the temp temper eratu ature re cha chara ract cter eris istic tic of of a nega negati tive ve temp temper eratu ature re coef coeffi fici cien entt therm thermis isto torr. tate the name of one other sensing device.
[2] [2] [!]
a
"escribe the structure of a metal#wire strain gauge.
[2]
b
A strain gauge contains !$ cm of wire of resistivit% $.& !&'( m. The resistance of the strain gauge is !$& . i ii
4
5
[2]
)alculate the cross#sectional area of the wire in the strain gauge. )alculate the increase in resistance when the wire extends b% &.! cm* assuming that the cross#sectional area and resistivit% remain constant.
[2] [!]
a
What is meant b% negative feedback ?
[2]
b
tate two advantages of negative feedback in an operational amplifier.
[2]
The circuit shown is used to produce a graph of V out out against V in in b% moving the slider on the variable resistor. The suppl% voltage to the op#amp is + V s.
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Worksheet
The graph obtained is shown.
a b c d
e
f
6
[2] [!] [!]
i s kept unchanged i Rin is halved in value but Rf is ii Rf is is halved in value but Rin is is unchanged from the initial value iii the suppl% voltage V s is is increased.
[2] [!] [!]
The variable resistor is removed and an a.c. signal of maximum voltage !.& 3 is applied to the input of the amplifier circuit. ketch the output voltage and input voltage on the same graph. 1xplain wh% the amplifier circuit produces distortion if an a.c. signal with a maximum voltage of 4.& 3 is applied to the input.
[2]
5n the circuit shown in 6uestion 5 the input voltage a b c d e
7
tate the t%pe of amplifier drawn. 1xplain how the graph shows that the amplifier is of this t%pe. tate wh% the graph flattens at the ends. uggest the value that was used for the suppl% voltage V s. tate what changes occur to the graph if
V in in is
[2]
!.& 3 and Rin is 2.& k .
1xplain wh% the potential at the inverting input 7 8 is almost 9ero. tate the value of the fall in potential across Rin. )alculate the current in Rin. 1xplain wh% the current in Rf is is the same as the current in Rin. "etermine the value of Rf . :ou :ou will need to use the graph from 6uestion 5.
[2] [!] [!] [!] [!]
An electrical device generates a potential of +!.& m3 at point P.
a b
tate two properties of an ideal operational amplifier. Assuming that the operational amplifier is ideal* calculate
[2]
the current in the !& k re resistor the potential at R the gain of the amplifier using %our answer to b ii the potential difference between R and and Q.
[2] [!] [!] [!]
i ii iii iv
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8
The circuit shows a non#inverting amplifier with an output voltage of ;.& 3. 3.
a b c d e 9
Worksheet
tate two differences between an op#amp used as an inverting amplifier and as a non#inverting amplifier. )alculate the gain of the amplifier shown in the circuit. )alculate the value of the input voltage V in in. )alculate the value of the current in the <& k re resistor. "etermine the voltage across the 2& k re resistor.
[2] [2] [!] [2] [!]
The circuit shows an op#amp used as a comparator. comparator.
a b c
1xplain how the op#amp acts as a comparator. [2] ' + tate the value of V out [!] out when V is larger than V . The resistors and the thermistors are all chosen to have the same resistance* as closel% as can be measured. i ii
1xplain wh% the value of V out is uncertain. out is The temperature of thermistor = falls. 1xplain what* if an%thing* happens to V '* V + and V out out.
[!] [4]
10 A device is to be placed on the output of the circuit shown in 6uestion 9* such that when the output voltage is +> 3 green light is emitted and when the output voltage is > 3 the light emitted is red. a b
"raw the circuit diagram of the device. 1xplain how the device works.
[2] [2]
Total
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