what are the social and economic impacts cryptocurrencies have ?
and how will this affect third world and poor countries because of their limited access to internet and modern technology?
Economic impact is that Bitcoin aims to remove the differences on foreign exchanges, it aims to have one common currency for the whole world and at least equalize every nation's wealth. Unlike current fiat currencies that rely on one country's gold reserve bitcoin don't have anything like that it is purely depending on the demand of it's users.
Other alt coins are created for some social purposes really depending on the coin.
The impact of Bitcoin is on the economy of Banks higher than other trade. Due to the popularity of Bitcoin people use bitcoin to exchange and make trade which directly make impact on Banks. Other Departments also impacted but not too much.