A 7.0 liter balloon at room temperature contains helium gas. if the temperature is halved, what happen to the volume?

The volume = 6.71 L

Charles's Law  

When the gas pressure is kept constant, the gas volume is proportional to the temperature  

V₁=7 L

T₁=25 °C(room temperature) + 273 = 298 K

T₂=12.5(halved) + 273 = 285.5 K

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current