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Standard Grade Physics. Unit 4 Electronics. Exercise. Label the following signals as analogue or digital. ( a ) ( b ) ( c ). analogue. analogue. digital. analogue. digital. analogue.

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Standard Grade Physics

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Standard Grade Physics

Unit 4 Electronics


Exercise

Label the following signals as analogue or digital.

(a) (b) (c)

analogue

analogue

digital


analogue

digital

analogue

(d) (e) (f)


Label following devices as analogue or digital.

(a) (b)

analogue

digital

(c) (d)

digital

analogue


sound

digital

sound

analogue

kinetic(rotation)

analogue

light

digital (analogue with variable R)

light

digital

light

digital

kinetic

digital

kinetic (in straight line)

digital


The solenoid.Set up the circuit as shown below:

Solenoid Unit

5 V

Touch lead here

“flying” lead

0 V


Negative sign on its side.

LED only allows current to flow and light up when “negative connected to negative”.


on

off

on

For a current to flow there has to be a difference in voltage.

on

off


10

VS– VLED

0∙015

12 – 2 = 10 V

667 Ω


VR = I R

VS– VR

 VR = 20 × 10-3 × 140

5 – 2∙8 = 2∙2 V

 VR = 2∙8 V


0 0 0 0

0 0 0 1

0 0 1 0

0 0 1 1

0 1 0 0

0 1 0 1

0 1 1 0

0 1 1 1

1 0 0 0

1 0 0 1


T.U.R.D.

temperature up resistance down

L.U.R.D.

light up resistance down


sound to electrical

light to electrical

heat to electrical


Capacitor Investigation

V

Potential divider

5 V

resistor

component investigations

0 V

capacitor

switch

With power off, discharge capacitor using switch so that V = 0 V. When power is switched on, start timer.


Conclusions:

The time to charge a capacitor depends on the values of the capacitance and the series resistor.

If the value of R and/or C are increased, the time taken to reach the final voltage also increases.

Comparison with waterCopy diagrams from P.T.A. page 107


Discharging a capacitor

The quickest and easiest way to discharge a capacitor is to place a wire across both ends of it.

5V

0V

charged

discharged


Copy the following table into the back of your jotter.


Set up the apparatus as shown below:

Potential divider

5 V

V1

resistor R1

V2

0 V

resistor R2

switch

Complete the table by measuring the voltage V1 and V2 for each pair of resistors.


24 + 12 = 36 Ω


V/R = 12/36 (leave as fraction to avoid rounding off)

12/36 x 24 = 8 V

12/36 x 12 = 4 V

8 244 = 12 = 2 (check!)


Step 1. RT = 1k + 5k = 6 kΩ

Step 2. I = V/R = 4∙5/6000

Step 3. V = I R

 V = 4∙5/6000x 5000

 V = 3∙75 V


Voltage across R= 6 – 2 = 4 V

V1 R1V2= R2

4 R2 = 4

2 x R = 4 x 4

 R = 16/2 = 8 Ω


Adjust the knob on the potentiometer until Vbe = required value. Now measure the corresponding Vout.

5 V

Potential divider

Transistor

Vout

0 V

4∙7 kpotentiometer

Vbe


Now draw a graph of your results.

Vout (V)

ON

OFF

Vbe (V)

0∙7 V


A current cannot flow through the collector unless a current flows through the base. For a current to flow through the base, Vbe≥ 0∙7 V.


RT = 1800 + 200 = 2 kΩ

I = V/R = 5/2000

V1 = Vbe = I R

 Vbe = 5/2000x 200= 0∙5 V

 Off

5 – 0∙5 = 4∙5 V

If temperature increases, resistance of thermistor decreases

 V across thermistor decreases and V across 200Ω increases

 V2 decreases and V1increases (V2 + V1 = 5 V)


0 V

5 V

2∙5 V


Remember:When the voltage divides, the resistor with the biggest value will take the biggest share of the voltage.

high

high

low

low

low

high


A temperature sensor.Set up the circuit as shown below:

Potential divider

Transistor

5 V

thermistor

0 V

4∙7 k pot.

Adjust potentiometer until LED is just off. Now warm thermistor by rubbing with your finger.


decreases

V across thermistor decreases

V across variable R increases

Vbe increases

Vbe≥ 0∙7 V, transistorswitches ON

LED is ON

reducing


high

high

low

low

low

high

dark


A light sensor.Set up the circuit as shown below:

Potential divider

Transistor

5 V

4∙7 k pot.

0 V

LDR

Adjust potentiometer until LED is just off. Now cover the LDR with your finger.


increases

voltage across LDR increases

Vbe increases

Vbe≥ 0∙7 V transistor switches on

LED is on

swap the

positions of the LDR and variable resistor.


The moisture unit.Set up the circuit as shown below:

200 k Ωsetting

Rain sensing unit

Ω

Observe what happens to the reading on the ohmmeter when water is added to the moisture unit.


high

high

low

low

low

high

dry


A moisture sensor. Set up the circuit shown below:

Potential divider

Transistor

5 V

Rain sensing unit

22k pot.

0 V

Turn the knob on the potentiometer fully clockwise. LED should be off. Now add water to the moisture unit.


increases

voltage across probes increases

Vbe increases

Vbe≥ 0∙7 V transistor switches on

LED is on

wet


0 V

5 V

5 V

0 V


A time-controlled circuit. Set up the circuit shown below:

Potential divider

Transistor

5 V

Capacitor

1000 μF

component investigations

4∙7 k pot.

switch

0 V

Press the switch to put the LED on. Release switch, LED will go off after a time delay.


discharges

voltage across C falls to 0 V immediately

voltage across R and Vbe rise to 5 V immediately

transistor switches on, current flows in relay, switch closes to complete circuit, motor and heater turn on.

charges

voltage across C rises to 5 V slowly

voltage across R and Vbe fall to 0 V slowly

Vbe  0∙7 V, transistor switches off, no current in relay, switch opens to break circuit, so motor and heater turn off.

Increase the value of R and/or C.


high

high

low

low

low

high


A switch controlled circuit. Set up the circuit shown below:

Potential divider

Transistor

5 V

switch

0 V

4.7 k pot.


high

V across switch = high

V across R = low

Vbe = low i.e.  0∙7 V, so transistor is off

low

V across switch = low

V across R = high

Vbe≥ 0∙7 V, transistor is on, current flows in relay, so relay switch closes to complete circuit


1

0

INVERTED (NOT the same as input)


A NOT (Inverter) gate. Set up the circuit shown below:

Debounced Switch

INVERTER

5 V

0 V


An OR gate. Set up the circuit shown below:

5 V

OR gate

0 V


0

1

1

1

A or B (or both) = 1


switch

lamp

switch


An AND gate. Set up the circuit shown below:

5 V

AND gate

0 V


Notes page 25

a n D

0

0

0

1

A and B = 1


master switch

motor

drivers’ switch


A

C

LDR

D

0

1

1

1

light

1

0

0

0

0

0

1

0

1

1

0

0

B

engine switch

A NOT gate is needed because the output from the LDR is ‘0’ in the dark.


A

D

LDR

E

F

light

B

IR detector

C

master switch


1

0

0

0

0

0

1

1

1

1

0

1

0

0

0

1

1

1

0

0

1

0

0

1


A clock pulse generator. Set up the circuit shown below:

5 V

Signal potentiometer

Inverter

1 kresistor

0 V

1000 Fcapacitor


0 V

0

1

5 V

off

rise

1

0

on

fall

0

1

off


decrease

computers, timers, clocks


A binary counter. Set up the circuit shown below:

5 V

0 V


Now replace the switch with a clock pulse generator:

5 V

Signal potentiometer

Counter

Inverter

1 kresistor

0 V

1000 Fcapacitor


An electronic counter with display and decoder. Set up the circuit shown below:

5 V

0 V


Output from light sensor in light = 0.X is an AND gate i.e. output will only be 1 when both inputs are logic 1.

5

0∙01s× 5= 0∙05 s

Length of the car.


TVs, radios, telephones, hi-fis, public announcement, intercom etc

Vo

Vg

Vin

Vo

Vg Vin

Vg = ?Vin = 5 mV

Vo = 0∙45 V

 Vg = Vo/Vin = 0∙45/(5 × 10–3)

 Vg = 90 (no unit)


Vg = 50Vin = 0∙1 V

Vo = ?

Vo

Vg Vin

 Vo = Vg× Vin

 Vo = 50 × 0∙1

 Vo = 5 V

100 Hz (no change in frequency)


Vpeak = 500 mV × 2

Vpeak = 2V × 3

 Vpeak = 1000 mV = 1V

Vpeak = 6V

 Vg = Vo/Vin = 6/1 =6


Po

Pg

Pin

Pg = 400Pin = 0∙01 W

Po = ?

Po

Pg Pin

 Po = Pg× Pin

 Po = 400 × 0∙01

 Po = 4 W


Pin = I V = 0∙005 × 0∙2 = 0∙001 W

Pout = I V = 0∙04 × 2 = 0∙08 W

Po 0∙08 Pg = Pin = 0∙001 = 80 (no unit needed)


V2P = R

V2

P

R

Vout2 R

Vin2 R


V2

Vin2 Pin = R

Po

 Po = Pg× Pin

P

R

Pg

Pin

(12 × 10-3)2 Pin = 10

 Po = 500 × 1∙44 × 10-5

 Pin = 1∙44 × 10-5 W

 Po = 7∙2 × 10-3 W


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