Logic circuit: gates, wires and junctions

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Quick Questions

Shade in the A or B circle for each question.

1. In a logic circuit diagram, where are the inputs normally drawn?

A On the right

B On the left

2. In a logic circuit diagram, where is the output X normally drawn?

A On the left

B On the right

3. Which statement about a wire in a logic circuit is correct?

A A wire carries either 0 or 1

B A wire can carry any number from 0 to 9

4. Which statement about a logic circuit is correct?

A The output of one gate can be the input of the next gate

B Each gate must take its inputs only from A, B or C

5. What does a dot where wires meet on a circuit diagram show?

A A junction where one wire splits into two

B A NOT gate that flips the value

Match the Pairs

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

Left column		Right column
1A ──┬──[AND]── X └──[NOT]──		AA, B, C -> gates -> X
2(A AND B) OR C		BThe inputs and output are on the wrong sides. Inputs go on the left and the output goes on the right.
3A wire carries only one of two values at any moment: 0 or 1		CA junction dot where the wire from input A splits, so the same 0 or 1 goes into two gates
4Inputs are drawn on the left and the output on the right, so the signal flows left to right		Dwire = 1
5Output X drawn on the left, inputs A and B drawn on the right		EThe AND gate output is wired into the OR gate as one of its inputs
6A wire from the output of an AND gate cannot go into another gate		FThis is false. The output of one gate can be joined by a wire to the input of the next gate.

Definitions

logic circuit

Fill in the Blanks

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

# X is 1 if W is 1 or C is 1 W = A AND B X = W __ C

# Gate 1 output W is input to gate 2 W = A AND B X = _ OR C

# Inputs A, B on left; output on right _ = A AND B

# Junction: A goes to both gates X = (A AND B) OR (NOT _)

A = 1, B = 1 W = A AND B # The wire W carries _

Spot the Error

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

Question 1

A Inputs A, B are on the left

B A and B feed an AND gate

C Wire W carries 0 to 9

D W goes to a NOT gate

E Output X is on the right

Question 2

A Inputs: A, B, C (left side)

B A and B go into a NOT gate

C OR output and C go to AND

D AND output is X (right side)

Question 3

A A is wired to two gates

B A dot shows where A turns to 1

C One copy goes to a NOT gate

D One copy goes to an AND gate

Question 4

A A = 1, B = 0

B Gate 1: A AND B gives W

C Gate 2: NOT W gives X

D W = 0, so X = 0

Question 5

A Inputs are on the right

B The output is on the right

C Gates are joined by wires

Answer Key

Logic circuit: gates, wires and junctions

Section A: Quick Questions

B — On the left

B — On the right

A — A wire carries either 0 or 1

A — The output of one gate can be the input of the next gate

A — A junction where one wire splits into two

Section B: Match the Pairs

A ──┬──[AND]── X └──[NOT]── → A junction dot where the wire from input A splits, so the same 0 or 1 goes into two gates

(A AND B) OR C → The AND gate output is wired into the OR gate as one of its inputs

A wire carries only one of two values at any moment: 0 or 1 → wire = 1

Inputs are drawn on the left and the output on the right, so the signal flows left to right → A, B, C -> gates -> X

Output X drawn on the left, inputs A and B drawn on the right → The inputs and output are on the wrong sides. Inputs go on the left and the output goes on the right.

A wire from the output of an AND gate cannot go into another gate → This is false. The output of one gate can be joined by a wire to the input of the next gate.

Section C: Definitions

logic circuit — A diagram of logic gates joined by wires. Inputs are on the left, the output is on the right, and each wire carries 0 or 1. A dot where a wire splits is a junction.

Section D: Fill in the Blanks

# X is 1 if W is 1 or C is 1
W = A AND B
X = W OR C

# Gate 1 output W is input to gate 2
W = A AND B
X = W OR C

# Inputs A, B on left; output on right
X = A AND B

# Junction: A goes to both gates
X = (A AND B) OR (NOT A)

A = 1, B = 1
W = A AND B
# The wire W carries 1

Section E: Spot the Error

C — A wire in a logic circuit carries only a 0 or a 1, so line 3 should say 'Wire W carries 0 or 1'.

B — A NOT gate has only one input, so it cannot take both A and B. The circuit needs a two-input gate here: 'A and B go into an OR gate'.

B — A junction dot only shows where a wire splits into copies. It does not change the value. Each copy carries the same 0 or 1 as A.

D — The NOT gate reverses its input. W is 0, so X = NOT 0 = 1. Line 4 should be 'W = 0, so X = 1'.

A — In a logic circuit the inputs are drawn on the left and the output on the right, so line 1 should say the inputs are on the left.