PhysicsA.gif

(New tips are continually added to these pages.  Check back in a few months' time for more)

TOPIC 15:    Atomic Structure and Radioactivity

Tip 1:

What is Binding Energy?

There are 2 definitions, both of which are acceptable although (1) is more preferred than (2) in recent years:

1.    Binding Energy is the work that needs to be done to completely separate a nucleus into individual nucleons.

2.    Binding Energy is the energy released when protons or neutrons combine to form the nucleus.

 

Tip 2:

In this chapter, I sometimes break a golden rule.

This golden rule is "When solving all physics problems, all units must be in SI base units:  All Time measurements MUST be in seconds; all Mass measurements in kilograms; and all Length measurements in metres"

However, when calculating the Decay Constant l it is sometimes acceptable to let its unit remain as "hour-1" "day-1" "month-1" or even "year-1" rather than "second-1"

This is because in the radioactive equations:

N = No exp (-lt) and A = Ao exp (-lt)

If we let the time t be in hour/day/month/year, so long as the units for the time (t) matches the reciprocal of the units for the decay constant (l), they will cancel out.  For example, if  l is in "day-1" and t is measured in days, they will cancel out to give a dimensionless constant.

However, do be careful...

When using the equation: A = lN to calculate the Activity in Becquerel (Bq), the Decay Constant l has be in "second-1".  This is because the activity rate (Bq) measures the "number of decays per second".  Not "per hour", "per day", "per month" or "per year"

Please watch out for this.

 

backA.gif

 

Copyright Physics.com.sg (Registration No. 52890077C).  All rights reserved.
First Class in Physics Tuition is the Registered Trademark (TM No. T02/02149B) of Physics.com.sg
.