Question

Please just give me an answer, thanks.
1. task
The resistance of the light bulb is 0.4 kΩ. To what voltage is it connected if a current of 33 mA flows through it? The answer is rounded to the nearest whole number!
2. task
The length of the cable is 69 m, its cross-sectional area is 0.4 mm2. What material is the wire made of if its resistance is 86.3 Ω? Just give me the result of numbers, i'll find myself what material corresponds to those numbers
3. task
Calculate the resistance of the galvanometer if a current of 6 μA flows through it and the voltage is 7 mV! Round to the nearest whole number!

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Answer 1

#1

$\\ \rm\dashrightarrow P=VI\implies V=\dfrac{P}{I}$

$\\ \rm\dashrightarrow V=\dfrac{0.4\times 10^3}{33\times 10^{-3}}$

$\\ \rm\dashrightarrow V=0.012\times 10^{-6}$

$\\ \rm\dashrightarrow V=12mV$

#2

$\\ \rm\dashrightarrow R=\rho \dfrac{\ell}{A}$

$\\ \rm\dashrightarrow \rho =\dfrac{RA}{\ell}$

$\\ \rm\dashrightarrow \rho=\dfrac{86.3(0.4\times 10^6)}{69}$

$\\ \rm\dashrightarrow \rho=0.5\times 10^{6}$

• It should be silicon

#3

Ohms law

$\\ \rm\dashrightarrow R=\dfrac{V}{I}$

$\\ \rm\dashrightarrow R=\dfrac{7(10^3)}{6(10^{-6})}$

$\\ \rm\dashrightarrow R=1.167\times 10^9\Omega$