A radioactive substance decays to 20% of its original level in 24 seconds. What

Question

A radioactive substance decays to 20% of its original level in 24 seconds. What is the half-life? a. 1, 900 seconds b. 320 seconds c. 44.1 seconds d. 10.3 seconds e. 2.4 seconds Complete the following fission process: ^235 U + 1^n rightarrow ^151 La + ______. Complete the following fusion process: ^4 He + ^28 Si rightarrow _____. If a galaxy's redshift implies a receding velocity of 2.6 times 10^6 m/s, the distance to the galaxy is inferred to be a. 150 Mpc b. 36 Mpc c. 3.6 Mpc d. 7.5 light-years e. 2.3 AU A double convex lens with right-hand surface curvature of R_2 = 30 cm and left-hand surface curvature of R_1 = 10 cm has a power of 2.3 diopters. What index of refraction is the material? What material could be used? What would be the magnification of an object 40 cm from the lens?

Explanation / Answer

17 )

using equation

N = No ( 1/2 )t/t1/2    

( 2 )t/t1/2 = 5

t1/2 = 24 X ln10 2 / ln10 5

t1/2 = 10.3 sec

Option " d " is correct

18 )

mass no left side = 235 + 1 = 236

mass no of missing element is = 236 - 151 = 85

so the fission can be written as

235U + 1 n ----- > 151 La + 85 Kr  

19 )

same like above

4 He + 28 Si ---- > 32 S

20 )

using V = Ho X D

2.6 X 106 = 70.4 X D

D = 2.6 X 106 = 70.4

D = 3.6 Mpc

Option " C " is correct

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