Straight-line amortisation of bonds traded at a premium/discount

CFA Level I FRA
#1

Can someone explain if I’m thinking of this problem correctly:

If traded at a premium, the amortisation will reduce the bond liability value. Interest Expense = Interest Payment - SL amortisation

If traded at a discount, the amortisation will increase the bond liability value. Interest Expense = Interest Payment + SL amortisation

This is in line with the general movements of the accounts if the effective interest rate method is used. But I still don’t quite understand the mechanism behind the accounting treatment.

#2

You have it correctly.

Straight-line amortization and effective interest rate amortization work the same way; the only differences are the specific amortization amounts each year. The differences generally aren’t big enough to cause concern.