[填空题]
A cell with emf $ϵ$ and internal resistance $r$ is connected to a variable resistor $R$, an ammeter and a voltmeter as shown.
Both meters are ideal, and the variable resistor can vary from 0 to $9Ω$.
1.Derive a relation for the power $P$ dissipated in the variable resistor in terms of the internal resistance $r$, emf $ϵ$ and the value of the variable resistor $R$.
The graph shows the variation of the power dissipated in the resistor R with the value of the resistance R.
The maximum dissipated power is when $R$ equals the internal resistance of the battery $r$.
2.Determine the values of the internal resistance $r$ and the emf $ϵ$ of the cell.r= ≪Ω≫
ϵ= ≪V≫
3.1.Calculate the smallest possible reading on the ammeter.I= ≪A≫
On the axes given, sketch the variation of the reading of the voltmeter with the reading of the ammeter for all values of the variable resistor $R$ and state the quantity represented by the gradient.
