102. OCR A Level (H046-H446) SLR15 – 1.4 Logic gates & truth tab

What does a NOT gate do to its input?

• Outputs true if exactly one input is true

• Outputs true if at least one input is true

• Outputs true if both inputs are true

• Reverses the input

Answer explanation

A NOT gate reverses the input, meaning it outputs the opposite of the input signal.

When does an AND gate output true?

• If both of its inputs are true

• If at least one of its inputs is true

• If exactly one of its inputs is true

• Never

Answer explanation

An AND gate outputs true only if both of its inputs are true, making the correct answer choice 'If both of its inputs are true'.

What is the output of an OR gate when both inputs are zero?

• 1

• 0

• False

• True

Answer explanation

The output of an OR gate is 1 only when at least one input is 1. If both inputs are 0, the output will be 0. Therefore, the correct answer is 0.

Which gate outputs true if one and only one of its inputs are true?

• AND gate

• XOR gate

• OR gate

• NOT gate

Answer explanation

XOR gate outputs true if one and only one of its inputs are true, making it the correct choice in this scenario.

How can you remember the symbol for an OR gate?

• It has a line crossing through the middle

• It fits around the O of an OR

• It fits neatly around the capital letter D of an AND

• The catalytic T fits nicely into the base

Answer explanation

The symbol for an OR gate fits around the letter O of an OR, making it easier to remember.

What is the boolean expression for a logic diagram with an AND gate followed by a NOT gate?

• A AND B

• NOT A AND B

• NOT (A AND B)

• A AND B OR NOT C

Answer explanation

The correct boolean expression for an AND gate followed by a NOT gate is NOT (A AND B), where the output of the AND gate is negated by the NOT gate.

What does the OCR clarification document state about candidates?

• They are not required to construct truth tables

• They only need to know about AND gates

• They should be able to construct logic gate diagrams from a boolean expression and vice versa

• They should focus solely on XOR gates

Answer explanation

The OCR clarification document states that candidates should be able to construct logic gate diagrams from a boolean expression and vice versa.

What are NAND and NOR gates known as?

• Basic logic gates

• Universal logic gates

• Secondary logic gates

• Tertiary logic gates

Answer explanation

NAND and NOR gates are known as Universal logic gates because they can be used to create any other type of logic gate.

What does a NOR gate do?

• Reverses the output of an OR gate

• Outputs true if both inputs are true

• Combines the inputs without changing them

• Outputs true if at least one input is true

Answer explanation

A NOR gate reverses the output of an OR gate, meaning it outputs true only when both inputs are false.

How can you represent the AND operation in boolean algebra?

• Using the > symbol

• Using the + symbol

• Using the up carrot (^) symbol

• Using the & symbol

Answer explanation

The AND operation in boolean algebra is represented using the up carrot (^) symbol.