Electric Circuits and Resistance: Physics 0625 (Cambridge O Level / IGCSE)

A charge of $18\text{ C}$ flows through a torch bulb in $6\text{ s}$. What is the current in the bulb?

A circuit is made from a battery of e.m.f. $6.0\text{ V}$ connected in series to two resistors, $R_1 = 8\,\Omega$ and $R_2 = 4\,\Omega$, and a single ammeter. The battery and the connecting wires have negligible resistance.

(a) Calculate the combined resistance of $R_1$ and $R_2$. [2]

(b) Calculate the reading on the ammeter. [2]

(c) State the potential difference across $R_2$. [1]

Two resistors, $R_1 = 6\,\Omega$ and $R_2 = 3\,\Omega$, are connected in parallel across a battery of e.m.f. $4.0\text{ V}$. The battery has negligible internal resistance.

(a) Show that the combined resistance of $R_1$ and $R_2$ is $2.0\,\Omega$. [2]

(b) Calculate the total current supplied by the battery. [2]

(c) Calculate the current through $R_2$, and explain why it is different from the current through $R_1$. [2]

A wire made from a particular metal has a length of $2.0\text{ m}$, a cross-sectional area of $0.50\text{ mm}^2$, and a resistance of $4.0\,\Omega$ at constant temperature.

(a) A second wire is made from the same metal, with the same cross-sectional area but a length of $5.0\text{ m}$. Calculate its resistance. [2]

(b) A third wire, made from the same metal and with a length of $2.0\text{ m}$, has half the cross-sectional area of the original wire. State the resistance of this third wire, and explain how you found your answer. [2]

(c) The main cables used to carry large currents from a power station are made thick rather than thin. Explain, in terms of resistance, why this reduces the energy wasted by the cables. [2]

A charge of $5.0\text{ C}$ passes through a resistor, transferring $40\text{ J}$ of electrical energy to the resistor as it does so. What is the potential difference across the resistor?

A filament lamp is connected to a $12\text{ V}$ d.c. supply. When the lamp is operating normally, a current of $0.40\text{ A}$ flows through it. What is the resistance of the lamp at this current?

A series circuit consists of a resistor $R_1 = 15\,\Omega$ connected to a component X of unknown resistance, and a battery of e.m.f. $10\text{ V}$. The battery has negligible internal resistance. The current in the circuit is $0.20\text{ A}$.

(a) Calculate the potential difference across $R_1$. [2]

(b) State how the potential differences across the components in a series circuit are related to the e.m.f. of the battery, and use this to calculate the potential difference across X. [2]

(c) Calculate the resistance of X. [1]

Two cells, each of e.m.f. $1.5\text{ V}$, are connected in series with each other and with a single resistor of resistance $5.0\,\Omega$. The cells and the connecting wires have negligible resistance.

(a) State the combined e.m.f. of the two cells. [1]

(b) Calculate the current in the resistor. [2]

(c) State the potential difference across the resistor, and explain how this value compares with the combined e.m.f. found in part (a). [1]

A circuit consists of a resistor $R_1 = 4.0\,\Omega$ connected in series with a parallel combination of two further resistors, $R_2 = 6.0\,\Omega$ and $R_3 = 12\,\Omega$. This series–parallel network is connected across a battery of e.m.f. $12\text{ V}$ that has negligible internal resistance.

(a) Calculate the combined resistance of $R_2$ and $R_3$. [2]

(b) Hence calculate the total resistance of the circuit. [1]

(c) Calculate the total current supplied by the battery. [2]

(d) Calculate the potential difference across the parallel combination of $R_2$ and $R_3$. [1]

Three resistors, $R_1 = 10\,\Omega$, $R_2 = 10\,\Omega$ and $R_3 = 5.0\,\Omega$, are connected in parallel with each other. What is the combined resistance of this parallel network?