1.half-life of a radioactive substance is 2 years. After how many years 75% of t

ID: 1374066 • Letter: 1

Question

1.half-life of a radioactive substance is 2 years. After how many years 75% of this substance does decay into other substances?

2. In nuclear fusion two smaller nuclei combine to create a larger nucleus? T/F

3. If an object loses electron it will be positivley charged. T/F

4. In nuclear reactions, the identities of the elements never change? T/F

5. When you connect two resistors in series, the voltage across those two resistors is always the same? T/F

6. North pole of a magnet repels all other north poles? T/F

1) % remaining = 100 - 75 = 25 % = 0.25

0.25 = 1 / 2n

n = - ln(0.25)/ln(2) = 2

no of half-lifes = 2

No of years taken = 2*thalf = 2*2 = 4 years

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2) Nuclear fusion : 2 or more nuclei combine to form a single nucleus

Answer is True

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3) Loss of electrons makes an object positively charged

Answer is True

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4) Normal chemical reactions , elements identity never change . But in nuclear reactions , element identity changes

Answer is True

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5) When we connect resistors in parallel , voltage across is same . If connected in series, voltage will be distributed

Answer is False

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6) Like poles repel and unlike poles attract .

Answer is True

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