Telling similar gate symbols apart

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Quick Questions

Shade in the A or B circle for each question.

1. A gate has the AND shape with a small circle on its output. Which gate is it?

A AND

B NAND

2. A gate has the OR shape with a small circle on its output. Which gate is it?

A XOR

B NOR

3. Which gate symbol is an OR shape with an extra curved line at the input side?

A XOR

B NOR

4. Which describes the NOT gate symbol?

A A triangle with a small circle on its output

B A triangle with an extra curved line at its input

5. What does the small circle on a gate's output mean?

A The output is inverted (NOT)

B The gate has three inputs

Match the Pairs

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

Left column		Right column
1AND gate symbol + small circle on the output		ANAND needs a small circle on the output. An AND shape without a circle is just AND.
2OR gate symbol + small circle on the output		BA NOR gate: it gives the opposite of OR, so the output is 1 only when both inputs are 0
3The XOR gate has no output circle. Its symbol is the OR shape with an extra curved line at the input side.		COR symbol + extra curved line at the inputs (no circle) = XOR
4The NOT gate is drawn as a triangle with a small circle on its output, and it has only one input.		DA circle on the output means NOT, so OR with a circle is NOR, not XOR. XOR has an extra curved line at the input side instead.
5Labelling an OR shape with a circle on the output as XOR		EA NAND gate: it gives the opposite of AND, so the output is 0 only when both inputs are 1
6Labelling an AND shape with no circle on the output as NAND		FTriangle with a circle on the output tip = NOT (A -> X)

Definitions

output circle

Fill in the Blanks

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

AND symbol + output circle = ____

OR symbol + output circle = ___

XOR symbol = OR symbol + extra ______ line

NOT symbol = triangle + small ______

NAND gate: AND with output circle X = ___ (A AND B)

Spot the Error

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

Question 1

A AND: flat back, round front

B NAND: AND shape, no circle

C OR: curved back, pointed tip

Question 2

A Draw the NOR symbol:

B Start with the OR shape

C Add a circle on the input

Question 3

A NOT gate symbol:

B Shape: triangle

C Point faces the output

D Small circle on the input

Question 4

A XOR: OR shape + small circle

B Extra line: input side

C XOR has no output circle

Question 5

A AND: no circle

B NAND: AND + circle

C OR: no circle

D NOR: AND + circle

Answer Key

Telling similar gate symbols apart

Section A: Quick Questions

B — NAND

B — NOR

A — XOR

A — A triangle with a small circle on its output

A — The output is inverted (NOT)

Section B: Match the Pairs

AND gate symbol + small circle on the output → A NAND gate: it gives the opposite of AND, so the output is 0 only when both inputs are 1

OR gate symbol + small circle on the output → A NOR gate: it gives the opposite of OR, so the output is 1 only when both inputs are 0

The XOR gate has no output circle. Its symbol is the OR shape with an extra curved line at the input side. → OR symbol + extra curved line at the inputs (no circle) = XOR

The NOT gate is drawn as a triangle with a small circle on its output, and it has only one input. → Triangle with a circle on the output tip = NOT (A -> X)

Labelling an OR shape with a circle on the output as XOR → A circle on the output means NOT, so OR with a circle is NOR, not XOR. XOR has an extra curved line at the input side instead.

Labelling an AND shape with no circle on the output as NAND → NAND needs a small circle on the output. An AND shape without a circle is just AND.

Section C: Definitions

output circle — A small circle on a gate's output means NOT: AND becomes NAND and OR becomes NOR. XOR has no circle; its symbol is OR with an extra curved line at the input side.

Section D: Fill in the Blanks

AND symbol + output circle = NAND

OR symbol + output circle = NOR

XOR symbol = OR symbol + extra curved line

NOT symbol = triangle + small circle

NAND gate: AND with output circle
X = NOT (A AND B)

Section E: Spot the Error

B — NAND is AND with a small circle on the output. Line 2 should say NAND: AND shape + circle, because without the circle it is just an AND gate.

C — The NOT circle goes on the gate's output, not the input. Line 3 should say Add a circle on the output.

D — The NOT symbol is a triangle with a small circle at its output tip. Line 4 should say the circle is on the output.

A — XOR is OR with an extra curved line at the input side, not a circle. A circle on the output would make it NOR.

D — NOR is OR with a circle on the output. AND with a circle is NAND. Line 4 should say NOR: OR + circle.