What is the main principle involved in a Voltaic cell?

An electric refrigerator rated $400 \ W$ operates $8 \ h$ per day. What is the cost of the energy to operate it for $30$ days at ₹ $3.00$ per $kWh$?

Derive the relation $R = R_{1} + R_{2} + R_{3}$ when three resistors $R_{1}, R_{2}$ and $R_{3}$ are connected in series in an electric circuit.

State Ohm's law. How can it be verified experimentally? Does it hold good under all conditions? Comment.

Draw a labelled circuit diagram showing three resistors $R_{1}, R_{2}$ and $R_{3}$ connected in series with a battery $(E)$,a rheostat $(Rh)$,a plug key $(K)$ and an ammeter $(A)$ using standard circuit symbols. Use this circuit to show that the same current flows through every part of the circuit. List two precautions you would observe while performing the experiment.

If you connect three resistors having values $2 \, \Omega$, $3 \, \Omega$, and $5 \, \Omega$ in parallel, will the value of total resistance be less than $2 \, \Omega$, greater than $5 \, \Omega$, or lie between $2 \, \Omega$ and $5 \, \Omega$? Explain.