1)In unitati cifra 4 nu se va lua in consideratie astfel primim
E²/r
In SI: V²/ohm
ohm=V/A , astfel
V²/ohm=V²/(V/A)=V*A
Raspuns: a.
2)Se da:
R=10ohm
I/Isc=1/10
r=?ohm
Formule:
I/Isc=1/10
[E/(R+r)]/(E/r)=1/10
Er/E(R+r)=1/10
r/(R+r)=1/10
(R+r)/r=10
(R/r)+1=10
R/r=9
r=R/9
Calcule:
r=10/9≈1,11ohm
3)Q=UIt
I=U/R
Q=t*U²/R
Raspuns: b.
5)Se da:
p=11,2*10⁻⁷Ωm
d=0,75mm=7,5*10⁻⁴m
U=120V
P=600W
l=?m
Formule:
R=p*l/S
l=R*S/p
S=πR²
S=π(D/2)²
S=πD²/4
P=U²/R
R=U²/P
I=U²πD²/4*p*P
Calcule:
l=120²*3,14*(7,5*10⁻⁴)²/4*11,2*10⁻⁷*600≈9,46m
Raspuns: d.
