Magnetic field sensor

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Quick Questions

Shade in the A or B circle for each question.

1. What does a magnetic field sensor detect?

A The presence and strength of a magnetic field

B The brightness of light in a room

2. A door alarm has a magnet on the door and a sensor on the frame. What happens when the door opens?

A The sensor detects a stronger field, so the alarm switches off

B The sensor no longer detects the magnet's field, so the alarm can sound

3. Which use of a magnetic field sensor is correct?

A A compass measuring the temperature of the air

B A compass finding the direction of the Earth's magnetic field

4. How can a magnetic field sensor help measure the speed of a wheel?

A It counts the pulses each time a magnet on the wheel passes by

B It measures how hot the wheel gets as it spins

5. Which device uses a magnetic field sensor to find buried metal?

A A metal detector

B A barcode scanner

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1magnetic field sensor		AA magnetic field sensor does not measure temperature. It detects the presence and strength of a magnetic field. A temperature sensor measures temperature.
2magnetic field strength		BThe data captured by a magnetic field sensor, which is sent to the microprocessor
3A door alarm uses a magnetic field sensor to detect when a magnet on the door moves away from the frame		CIF magnetic_sensor < 5 THEN sound_alarm()
4A metal detector uses a magnetic field sensor to detect a change in the magnetic field caused by metal		DAn input device that detects the presence and strength of a magnetic field
5A magnetic field sensor measures the temperature of a room		EA wheel speed counter uses a magnetic field sensor to detect a magnet on the wheel passing by each turn, not light.
6Wheel speed counter: sensor detects light from the wheel		FIF field_strength > 80 THEN beep()

Definitions

magnetic field sensor

Fill in the Blanks

Complete each line of code by filling in the missing parts.

strength ← ____(magneticSensor)

heading ← READ(compassSensor) ______ heading

IF fieldStrength _ 10 THEN alarm ← ON ENDIF

IF magnetDetected = TRUE THEN rotations ← _________ + 1 ENDIF

IF strength > 80 ____ OUTPUT "Metal found" ENDIF

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A field ← READ(magSensor)

B IF field < 10 THEN

C alarm ← OFF

D ENDIF

Question 2

A field ← READ(magSensor)

B IF field >= 10 THEN

C OUTPUT "Window open"

D ELSE

E OUTPUT "Window open"

F ENDIF

Question 3

A field ← READ(magSensor)

B heading ← DIRECTION(light)

C OUTPUT heading

Question 4

A count ← 0

B IF READ(magSensor) < 5 THEN

C count ← count + 1

D ENDIF

Question 5

A baseline ← 20

B field ← READ(magSensor)

C IF field > baseline THEN

D SOUND(keyboard)

E ENDIF

Answer Key

Magnetic field sensor

Section A: Quick Questions

A — The presence and strength of a magnetic field

B — The sensor no longer detects the magnet's field, so the alarm can sound

B — A compass finding the direction of the Earth's magnetic field

A — It counts the pulses each time a magnet on the wheel passes by

A — A metal detector

Section B: Match the Pairs

magnetic field sensor → An input device that detects the presence and strength of a magnetic field

magnetic field strength → The data captured by a magnetic field sensor, which is sent to the microprocessor

A door alarm uses a magnetic field sensor to detect when a magnet on the door moves away from the frame → IF magnetic_sensor < 5 THEN sound_alarm()

A metal detector uses a magnetic field sensor to detect a change in the magnetic field caused by metal → IF field_strength > 80 THEN beep()

A magnetic field sensor measures the temperature of a room → A magnetic field sensor does not measure temperature. It detects the presence and strength of a magnetic field. A temperature sensor measures temperature.

Wheel speed counter: sensor detects light from the wheel → A wheel speed counter uses a magnetic field sensor to detect a magnet on the wheel passing by each turn, not light.

Section C: Definitions

magnetic field sensor — An input device that detects the presence and strength of a magnetic field. Used in door alarms, compasses, wheel speed counters and metal detectors.

Section D: Fill in the Blanks

strength ← READ(magneticSensor)

heading ← READ(compassSensor)
OUTPUT heading

IF fieldStrength < 10 THEN
    alarm ← ON
ENDIF

IF magnetDetected = TRUE THEN
    rotations ← rotations + 1
ENDIF

IF strength > 80 THEN
    OUTPUT "Metal found"
ENDIF

Section E: Spot the Error

C — When the door opens, the magnet moves away and the sensor reads a weak field. The alarm must turn ON, so the line should be alarm ← ON.

C — A strong field means the magnet is next to the sensor, so the window is closed. This line should output "Window closed".

B — A compass works out direction from the magnetic field reading. The variable light does not exist, so it should be DIRECTION(field).

B — A magnet on the wheel gives a strong field each time it passes the sensor. The condition should test for a strong reading (> 50), not a weak one.

D — A metal detector gives a sound alert through an output device. A keyboard is an input device, so it should be SOUND(speaker).