The bulb

What is the resistance of a filament lamp when it is connected to a 9V battery and has a current of 120 mA?

Correct result:

R =  75 Ω

Solution:

$$\begin{gathered} U=9\text{ V } \\ I=120\text{ mA}\to \text{ A}=120\mathrm{/}1000\text{ A}=0.12\text{ A } \\ R=U\mathrm{/}I=9\mathrm{/}0.12=75\mathrm{\Omega } \end{gathered}$$

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