1.
U=230 V
I=400 mA = 0,4 A
R = ?
Z prawa Ohma
[tex]I=\frac{U}{R} \ \ \rightarrow \ \ R=\frac{U}{I}=\frac{230 \ [V]}{0,4 \ [A]}=575 \ \Omega[/tex]
2.
P=0,345 kW = 345 W
a)
t=20 min = 1/3 h = 1200 s
E = ?
[tex]E=P*t=0,345 \ [kW]*\frac{1}{3} \ [h]=0,115 \ kWh\\ \\1 \ [J]=1 \ [W]*[s]\\ \\E=P*t=345 \ [W]*1200 \ [s]=414000 \ J=414 \ kJ=0,414 \ MJ[/tex]
b)
U=230 V
I = ?
[tex]P=U*I \ \ \rightarrow \ \ I=\frac{P}{U}=\frac{345 \ [W]}{230 \ [V]}=1,5 \ A[/tex]
c)
t=10 h
c=50 gr/kWh
k = ?
[tex]k=P*t*c=0,345 \ [kW]*10 \ [h]*50 \ [\frac{gr}{kWh}]=172,5 \ gr=1,73 \ PLN[/tex]
3.
U=15 V
q=8 C
W = ?
[tex]W=P*t=U*I*t\\ \\I=\frac{q}{t}\\ \\W=U*\frac{q}{t}*t=U*q=15 \ [V]*8 \ [C]=120 \ J\\ \\1 \ [V]=\ [\frac{W}{A}]=[\frac{J}{C}][/tex]
