Vipul Singh

A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing. 

Commonly used material are copper, zinc, aluminium. Fuse works on I^2 x R principle. The heat developed by excess current will melt the fuse wire. Eg. At full load your house/motor/ appliance draws a specific amount of current lets say 5Amps. So fuse wire is set to a bit higher value like 5.5/6/7 Amps. 5Amps is not selected because you need 5A for the appliance to work, at 5A the fuse will burn. So you select a value slightly higher than 5Amps. You want the fuse wire to melt above 5Amps so that your device is not damaged. In this way your appliance is protected.

The causes of the Great Depression were
(i) Conditions created by war There was an immense industrial expansion due to the increased demand of goods supplied to the army, during the period of the First World War. After the war, the demand for these goods suddenly dropped and so, there was no demand in many industries. There was also a large fall in the agricultural prices due to reduced demand.
(ii) Over production in agriculture Agricultural over production was another major factor responsible for the depression. This was made worse by falling agricultural .prices. As prices slumped and agricultural incomes declined, the farmers tried to increase the production and bring a larger volume of produce to the market to maintain their overall income. This worsened the situation by pushing down the prices of farm produce further.
(iii) Shortage of loans In the mid-1920s, many countries financed their investments through loans from the USA. While it was often very easy to raise loans in the USA during the boom period, lenders in the USA panicked at the first sign of trouble. Countries that depend crucially on US loans, now faced an acute crisis.
(iv) Multiple effect With the fall in prices and the prospect of a depression i.e. banks in the USA slashed domestic lending and some stopped bank loans, thousands of banks went bankrupt and were forced to close down. Factories closed, leading to unemployment, which further aggravated the crises. The US banking system collapsed.
(v) Large-scale unemployment Farm could not sell their harvests, businesses collapsed. As a result, large scale unemployment occurred.