# IGCSE Physics Paper-2: Specimen Questions with Answers 6 - 9 of 20

## Question number: 6

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### Write in Short

Define half – life of radioactive substance and give appropriate formula for half – life time.

### Explanation

Half – life of radioactive substance is defined as, “The time required for amount of radioactive substance to fall to half of its initial value. “

The exponential decay can be described by following equation,

Where, N = Quantity of the radioactive substance still remaining after a time t

Initial quantities of the radioactive substance

Now, for half life time,

## Passage

Two resistors are connected in parallel with 10 V power supply in circuit given below

## Question number: 7 (1 of 3 Based on Passage) Show Passage

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### Write in Short

Calculate the current I, passing through the circuit,

### Explanation

Total current in the circuit is calculated by Ohm’s law as,

## Question number: 8 (2 of 3 Based on Passage) Show Passage

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### Write in Short

Calculate the combined resistance of the resistors.

### Explanation

For parallel resistors, equivalent resistor can be calculated as,

Here, both resistors are of same resistance,

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