Capacitive touch screen

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Quick Questions

Shade in the A or B circle for each question.

1. What does a capacitive touch screen detect when you touch it?

A The pressure of two plastic layers being pushed together

B A change in the electrical charge of the glass layer at the touch point

2. Why does a bare finger work on a capacitive touch screen?

A A finger conducts electricity and disturbs the screen's electric field

B A finger is warm enough to melt the top layer of the screen

3. A student taps a capacitive screen with an ordinary woolly glove. What usually happens?

A Nothing, because the glove does not conduct electricity

B It works perfectly, because the screen senses pressure

4. Which tool would NOT normally work on a capacitive touch screen?

A A bare finger

B An ordinary plastic stylus

5. Which gesture can a capacitive touch screen support?

A Pinching two fingers to zoom (multi-touch)

B Only one touch point at a time

Match the Pairs

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

Left column		Right column
1capacitive touch screen		ACapacitive screens need a conductive object such as a finger. Plastic does not conduct electricity, so it cannot change the charge.
2multi-touch		Bglove or plastic stylus -> no charge change -> no touch
3A finger conducts electricity, so it disturbs the screen's electric field at the touch point and the position is found		CA touch screen with a charged glass layer. A finger conducts electricity and changes the charge at the touch point, so its position is found.
4Ordinary gloves and a plastic stylus do not conduct electricity, so a capacitive screen does not respond to them		Dfinger touch -> charge changes -> position found
5Capacitive screens work with any object, such as a plastic stylus		EThis describes a resistive screen. A capacitive screen finds the touch point from the change in charge caused by a conductive finger.
6A capacitive screen finds the touch point when two layers are pressed together		FThe screen can detect two or more fingers at the same time, which allows gestures such as pinching to zoom in or out.

Definitions

capacitive touch screen

Fill in the Blanks

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

IF finger = TRUE ____ chargeChanges ← TRUE

IF glove = "ordinary" THEN touch ← _____

IF touchCount _ 1 THEN multiTouch ← TRUE

change ← chargeBefore - ___________

______ "Pinch to zoom uses multi-touch"

Spot the Error

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

Question 1

A layer <- 'plastic film'

B finger <- TRUE

C IF finger THEN

D PRINT 'Charge changes'

E ENDIF

Question 2

A object <- 'plastic stylus'

B works <- TRUE

C PRINT works

Question 3

A glove <- 'ordinary'

B IF glove = 'ordinary' THEN

C PRINT 'Touch detected'

D ENDIF

Question 4

A device <- 'smartphone'

B screen <- 'resistive'

C PRINT device, screen

Question 5

A finger_touch <- TRUE

B IF finger_touch = TRUE

C PRINT 'Find touch position'

D ENDIF

Answer Key

Capacitive touch screen

Section A: Quick Questions

B — A change in the electrical charge of the glass layer at the touch point

A — A finger conducts electricity and disturbs the screen's electric field

A — Nothing, because the glove does not conduct electricity

B — An ordinary plastic stylus

A — Pinching two fingers to zoom (multi-touch)

Section B: Match the Pairs

capacitive touch screen → A touch screen with a charged glass layer. A finger conducts electricity and changes the charge at the touch point, so its position is found.

multi-touch → The screen can detect two or more fingers at the same time, which allows gestures such as pinching to zoom in or out.

A finger conducts electricity, so it disturbs the screen's electric field at the touch point and the position is found → finger touch -> charge changes -> position found

Ordinary gloves and a plastic stylus do not conduct electricity, so a capacitive screen does not respond to them → glove or plastic stylus -> no charge change -> no touch

Capacitive screens work with any object, such as a plastic stylus → Capacitive screens need a conductive object such as a finger. Plastic does not conduct electricity, so it cannot change the charge.

A capacitive screen finds the touch point when two layers are pressed together → This describes a resistive screen. A capacitive screen finds the touch point from the change in charge caused by a conductive finger.

Section C: Definitions

capacitive touch screen — A touch screen with a charged glass layer. A finger conducts electricity and changes the charge at the touch point, so its position is found. Supports multi-touch.

Section D: Fill in the Blanks

IF finger = TRUE THEN chargeChanges ← TRUE

IF glove = "ordinary" THEN touch ← FALSE

IF touchCount > 1 THEN multiTouch ← TRUE

change ← chargeBefore - chargeAfter

OUTPUT "Pinch to zoom uses multi-touch"

Section E: Spot the Error

A — A capacitive touch screen uses a charged glass layer, not a plastic film. The line should be layer <- 'charged glass'.

B — A plastic stylus does not conduct electricity, so it cannot change the charge on a capacitive screen. works should be FALSE.

C — Ordinary gloves are insulators, so they do not change the charge at the touch point. The touch is not detected.

B — Smartphones and tablets use capacitive touch screens. The line should be screen <- 'capacitive'.

B — The IF statement is missing THEN. It should be IF finger_touch = TRUE THEN.