A student investigates an electrical circuit. The circuit is set up as shown in Fig. 2.1. A battery of negligible internal resistance is connected to a resistor of resistance $$$Z$$$. Five resistors, each of resistance $$$R$$$, are connected in parallel between P and Q . The switch is closed. The total current $$$I$$$ in the circuit is measured using the ammeter. The experiment is then repeated by changing the number $$$n$$$ of resistors, each of resistance $$$R$$$, connected in parallel between P and Q . It is suggested that $$$I$$$ and $$$n$$$ are related by the equation $$\[ E=I\left(\frac{R}{n}+Z\right) \]$$ where $$$E$$$ is the electromotive force (e.m.f.) of the battery. （b）Values of $$$n, \frac{1}{n}$$$ and $$$I$$$ are given in Table 2．1． Calculate and record values of $$$\frac{1}{I} / 10^{3} \mathrm{~A}^{-1}$$$ in Table 2．1．Include the absolute uncertainties in $$$\frac{1}{I}$$$ ．［2］

Physics

IGCSE&ALevel

CAIE

Exam No：9702_s25_qp_53 Year：2025 Question No：2(b)

Answer:

Knowledge points:

1.3.1 understand that the avogadro constant Na is the number of atoms in 0.012kg of carbon-12

1.3.2 use molar quantities where one mole of any substance is the amount containing a number of particles equal to the avogadro constant Na

10.1.1 recall and use appropriate circuit symbols as set out in the ASE publication Signs, Symbols and Systematics (example circuit symbols are given in Section 5.5.)

10.1.2 draw and interpret circuit diagrams containing sources, switches, resistors, ammeters, voltmeters, and/or any other type of component referred to in the syllabus

10.1.3 define electromotive force (e.m.f.) in terms of the energy transferred by a source in driving unit charge round a complete circuit

10.1.4 distinguish between e.m.f. and potential difference (p.d.) in terms of energy considerations

10.1.5 understand the effects of the internal resistance of a source of e.m.f. on the terminal potential difference

Answer:

Knowledge points:

Solution:

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