(a) Definition of Supply: “Supply refers to the quantity of a commodity offered for sale at a given price in a given market at a given time.” In simple words, supply means that quantity of a particular commodity which a seller is ready to sell at a given price. It is the price which vitally affects the supply of goods. 

The rightward shift of the supply curve denotes the increase in supply. Increase in supply is a situation when quantity supplied increases due to the favourable changes in factors other than price. 

The reasons for rightward shift of the supply curve are as under: 

1. Fall in the price of factors of Production: When prices of factors of production (wages, cost of raw material etc.) decreases, it increases the profit margin of produce seller which induces him to increase the supply. 

2. Increase in the number of firms in the Market: When new firms enter into the market then total supply increases. 

3. When the firm expects a fall in the Price of the Commodity: If firms expects that in near future prices are going to be decreased then they increase their present supply at higher prices in order to fetch out more and more profits.

(b) Public Debt: Public Debt refers to “Obligation of Government particularly those evidenced by securities, to pay certain sums to the holders at some future date. In,simple words, Public Debt can be defined as the amount of debt taken by government from internal as well as external sources to meet out its deficit. Government needs to borrow when current revenue falls short of public expenditure. 

Types of Public Debt 

1. Internal and External Debt: Public loans floated within the country, are called Internal Debt. Public borrowings from other countries, are referred to as External Debt. External debt permits import of real resources. It enables the country to consume more then it produces. The sources of internal debts are RBI, commercial banks, etc. and of external debts are loans from foreign government, IMF, World Bank etc. 

2. Productive and Unproductive Debt: When government borrows for development expenditure like on power projects, establishing heavy industries, etc. so that it generates revenue then the debt is productive. When government borrows for non-development uses, such as war finance, etc. the debt becomes unproductive as it does not create any income in return. 

3. Compulsory and Voluntary Debt: When government borrows from people by using coercive methods, loans so raised are referred to as compulsory public debts, e.g. Tax. When government floats loans by issuing securities, the members of the public and institutions like commerial banks may subscribe to them. e.g. Public Borrowings. 

4. Redeemable and Irredeemable Debt: Loans which the govt, promises to pay off at some future date are called redeemable debts. Loans for which no promise is made by the government regarding the exact date of maturity and all that the govt, does is to agree to pay interest regularly for the bonds issued, are called irredeemable debts.