Magnetic field strength

Opportunity cost
The true cost of something is what you give up to get it.(This includes not only the money spent in buying (or doing) the something, but also the economic benefits (UTILITY) that you did without because you bought (or did) that particular something and thus can no longer buy (or do) something else.)
 Factors of production
The ingredients of economic activity: land, labor, capital and enterprise.
Economic Development
The scope of economic development includes the process and policies by which a nation improves the economic, political, and social well-being of its people.
 Substitute goods
Goods for which an increase (or fall) in DEMAND for one leads to a fall (or increase) in demand for the other – Coca-Cola and Pepsi, perhaps.
Cross Price Elasticity of Demand
In economics, the cross elasticity of demand or cross-price elasticity of demand measures the responsiveness of the demand for a good to a change in the price of another good.
([QDemand(NEWX) - QDemand(OLDX)] / QDemand(OLDY))/ [Price(NEWY5) - Price(OLDY)] / Price(OLDY)
 Normal goods
When average INCOME increases, the DEMAND for normal goods increases, too. The opposite of INFERIOR GOODS.
 Elasticity
A measure of the responsiveness of one variable to changes in another. Economists have identified four main types.
PRICE ELASTICITY measures how much the quantity of SUPPLY of a good, or DEMAND for it, changes if its PRICE changes. If the percentage change in quantity is more than the percentage change in price, the good is price elastic; if it is less, the good is INELASTIC.
INCOME elasticity of demand measures how the quantity demanded changes when income increases.
Cross-elasticity shows how the demand for one good (say, coffee) changes when the price of another good (say, tea) changes. If they are SUBSTITUTE GOODS (tea and coffee) the cross-elasticity will be positive: an increase in the price of tea will increase demand for coffee. If they are COMPLEMENTARY GOODS