Why does dns use udp instead of tcp? if a dns packet is lost, there is no automatic recovery. what are the consequences?

If a DNS packet using UDP is lost this problem must be handled at the application layer. If an answer is not received after some period of time the specific application may choose to resend the DNS query. I can go much more into detail but this should answer your question. If you need more detail just ask.

Your background picture should be spiral

The amount of current is measured in units calledamperes or amps. one ampere of current is equal to the chargeof 6,240,000,000,000,000,000 electrons flowing past a given pointin a circuit per second