First time here! I got a question on a test that I cant get my head around.

enter image description here

  • How do I calculate value of R2 ?
  • Is it possible ?

Thanks in advance !

  • \$\begingroup\$ There's a built-in schematic editor on this site, if you want to make your schematic look nicer. \$\endgroup\$ – Hearth Mar 12 '19 at 15:26
  • 1
    \$\begingroup\$ Yes it's possible. You have three equations and constraints. HINT: Solve for the power dissipation of R2 in terms of I. Another hint: R2 is between 50 and 100 ohms, and the loop current is less than 250mA \$\endgroup\$ – BB ON Mar 12 '19 at 15:35
  • \$\begingroup\$ Thanks! I think i got it now! \$\endgroup\$ – Simon Watti Mar 12 '19 at 16:03

Express the current through the circuit in function of R2:

$$ I = \frac{10 V}{R_2 + 15 \Omega} $$

Express power dissipated in the second resistor in function of the current and resistance:

$$ 1W = P = I^2R_2 = \biggl(\frac{10 V}{R_2 + 15 \Omega}\biggl)^2 \times\ R_2 $$

Solve for resistance, solve for current, solve for other resistance's dissipated power.

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