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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

Standard Grade Physics

Unit 4 Electronics


Standard grade physics

Exercise

Label the following signals as analogue or digital.

(a) (b) (c)

analogue

analogue

digital


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analogue

digital

analogue

(d) (e) (f)


Standard grade physics

Label following devices as analogue or digital.

(a) (b)

analogue

digital

(c) (d)

digital

analogue


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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

The solenoid.Set up the circuit as shown below:

Solenoid Unit

5 V

Touch lead here

“flying” lead

0 V


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Negative sign on its side.

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


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on

off

on

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

on

off


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10

VS– VLED

0∙015

12 – 2 = 10 V

667 Ω


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VR = I R

VS– VR

 VR = 20 × 10-3 × 140

5 – 2∙8 = 2∙2 V

 VR = 2∙8 V


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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


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T.U.R.D.

temperature up resistance down

L.U.R.D.

light up resistance down


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sound to electrical

light to electrical

heat to electrical


Capacitor investigation

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.


Standard grade physics

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


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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


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Copy the following table into the back of your jotter.


Set up the apparatus as shown below

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.


Standard grade physics

24 + 12 = 36 Ω


Standard grade physics

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!)


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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


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Voltage across R= 6 – 2 = 4 V

V1 R1V2= R2

4 R2 = 4

2 x R = 4 x 4

 R = 16/2 = 8 Ω


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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

Now draw a graph of your results.

Vout (V)

ON

OFF

Vbe (V)

0∙7 V


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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.


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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)


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0 V

5 V

2∙5 V


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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

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.


Standard grade physics

decreases

V across thermistor decreases

V across variable R increases

Vbe increases

Vbe≥ 0∙7 V, transistorswitches ON

LED is ON

reducing


Standard grade physics

high

high

low

low

low

high

dark


A light sensor set up the circuit as shown below

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.


Standard grade physics

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

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.


Standard grade physics

high

high

low

low

low

high

dry


A moisture sensor set up the circuit shown below

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.


Standard grade physics

increases

voltage across probes increases

Vbe increases

Vbe≥ 0∙7 V transistor switches on

LED is on

wet


Standard grade physics

0 V

5 V

5 V

0 V


A time controlled circuit set up the circuit shown below

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.


Standard grade physics

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.


Standard grade physics

high

high

low

low

low

high


A switch controlled circuit set up the circuit shown below

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

Potential divider

Transistor

5 V

switch

0 V

4.7 k pot.


Standard grade physics

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


Standard grade physics

1

0

INVERTED (NOT the same as input)


Standard grade physics

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

Debounced Switch

INVERTER

5 V

0 V


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An OR gate. Set up the circuit shown below:

5 V

OR gate

0 V


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0

1

1

1

A or B (or both) = 1


Standard grade physics

switch

lamp

switch


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An AND gate. Set up the circuit shown below:

5 V

AND gate

0 V


Standard grade physics

Notes page 25

a n D

0

0

0

1

A and B = 1


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master switch

motor

drivers’ switch


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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.


Standard grade physics

A

D

LDR

E

F

light

B

IR detector

C

master switch


Standard grade physics

1

0

0

0

0

0

1

1

1

1

0

1

0

0

0

1

1

1

0

0

1

0

0

1


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

5 V

Signal potentiometer

Inverter

1 kresistor

0 V

1000 Fcapacitor


Standard grade physics

0 V

0

1

5 V

off

rise

1

0

on

fall

0

1

off


Standard grade physics

decrease

computers, timers, clocks


Standard grade physics

A binary counter. Set up the circuit shown below:

5 V

0 V


Standard grade physics

Now replace the switch with a clock pulse generator:

5 V

Signal potentiometer

Counter

Inverter

1 kresistor

0 V

1000 Fcapacitor


Standard grade physics

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

5 V

0 V


Standard grade physics

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.


Standard grade physics

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)


Standard grade physics

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)


Standard grade physics

Vpeak = 500 mV × 2

Vpeak = 2V × 3

 Vpeak = 1000 mV = 1V

Vpeak = 6V

 Vg = Vo/Vin = 6/1 =6


Standard grade physics

Po

Pg

Pin

Pg = 400Pin = 0∙01 W

Po = ?

Po

Pg Pin

 Po = Pg× Pin

 Po = 400 × 0∙01

 Po = 4 W


Standard grade physics

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)


Standard grade physics

V2P = R

V2

P

R

Vout2 R

Vin2 R


Standard grade physics

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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