Mechanical and electrical
Answer:
- Direct current is a current in which electrons flow in one direction only
- Alternating current is a current in which the direction of the electron flow reverses periodically - so, half a cycle forward, half a cycle backward
There are several advantages of using alternating currents for the transmission of electricity across a country, over large distances. The main advantages are:
- The voltage of alternating currents can be easily increased/decreased by using transformers. For instance, a transformer is used at the beginning of the transmission line to increase the voltage (electricity is transmitted at high voltage in order to reduce dissipated power), and then another transformer is used before the electricity enters the houses, in order to decrease the voltage. Transformers only work with alternating currents.
- It is easy to interrupt the flow of an alternating current, because its value naturally becomes zero every half a cycle, so this is useful in case the current must be interrupted.
Answer:
52.47706 mph
54.5 mph
Explanation:
The average speed is given by
Julie's average speed on the way to Grandmother's house is 52.47706 mph
Average speed on the return trip is 54.5 mph
11:C) sound travels fastest in solids
12:A) Sound needs a medium to travel
13:D) Just like with cupped hands
