Current, Voltage and Resistance

Describe all the changes to the circuit in Fig. 5.1 that are needed so that the meters produce readings that can be used to calculate the resistance of the length of wire.

Calculate the resistance of the 9.0 cm length of wire.

resistance = ______ $\Omega$

Explain whether line Q is obtained with a length of wire that is longer or shorter than 9.0 cm.

Calculate the length of the wire used to obtain line Q.

length = ______ $\text{cm}$

Describe how a direct current differs from an alternating current (a.c.).

Calculate the charge that flows through point P in the time of $120\ \text{s}$.

charge = ______ $\text{C}$

The current in the circuit is due to the flow of electrons. Each electron carries a charge of magnitude $1.6 \times 10^{-19}\ \text{C}$.

State the direction which the electrons move past point P and determine the number of electrons that pass point P in $1.0\ \text{s}$.

direction ______

number of electrons = ______

Define the term 'electromotive force'.

Each battery consists of 92 cells in series.

Calculate the e.m.f. of one battery.

e.m.f. = ______ $\text{V}$

The power supply is made by connecting 85 of these batteries in parallel.

State the e.m.f. of the power supply.

e.m.f. = ______ $\text{V}$

the current in the lamp

current = ______ A

the resistance of the lamp in this circuit.

resistance = ______ $\Omega$

Fig. 7.1 shows the battery and the filament lamp.

On Fig. 7.1, complete the circuit diagram of a suitable circuit.

You will need to add additional components.

On Fig. 7.2, draw the shape of the current–voltage graph for the filament lamp.

State what happens to the resistance of a filament lamp as the applied voltage increases and explain one reason for this happening.

The reading on ammeter $\text{A}_1$ is $0.25\text{ A}$.

The reading on voltmeter $\text{V}_1$ is $3.0\text{ V}$.

Determine the readings on the other meters.

reading on ammeter $\text{A}_2$ = ______ $\text{A}$
reading on ammeter $\text{A}_3$ = ______ $\text{A}$
reading on voltmeter $\text{V}_2$ = ______ $\text{V}$

Calculate the resistance of resistor R.

resistance of resistor R = ______ $\Omega$

The resistor obeys Ohm's law.

State Ohm's law.

Fig. 6.2 shows the current–voltage graph for the filament lamp.

The battery in Fig. 6.1 is replaced with a different battery which has a different e.m.f. (electromotive force).

The voltage across the lamp increases to $6.0\text{ V}$.

Use data from the graph to determine the e.m.f. of the second battery.

Show your working.

e.m.f. = ______ $\text{V}$

Fig. 9.2 shows an incomplete circuit diagram of the circuit that a student uses to obtain the readings for the graph.

Complete the circuit diagram using suitable circuit symbols for the lamp, a voltmeter and a variable resistor.

The ammeter used by the student has ranges $0-10\text{ A}$, $0-1\text{ A}$, $0-100\text{ mA}$ and $0-10\text{ mA}$.

Describe how the student uses the different ranges to obtain readings which allow all nine points to be plotted precisely on the graph while using the ammeter safely.

State how Fig. 9.1 shows that the lamp does not obey Ohm's law.

the voltmeter reading is $0.40\text{ V}$

resistance = ______

the voltmeter reading is $6.0\text{ V}$.

resistance = ______

Explain why the resistance of the lamp changes as the voltage changes.

State how the resistance of a wire depends upon its length and how it depends on its cross-sectional area.

length ______
cross-sectional area ______

The student obtains a long sample of the same type of wire as the filament in the lamp.

The wire he obtains has the same cross-sectional area as the filament.

He cuts a $1.0\text{ m}$ length of the wire and measures its resistance at room temperature.

He obtains the value $16\ \Omega$.

Using the appropriate resistance value from (d), estimate the length of the filament wire in the lamp.

length = ______

The battery consists of three identical cells in series.

Determine the e.m.f. of each cell.

e.m.f. of each cell = ______

State what is meant by potential difference.

Calculate the resistance of the variable resistor.

resistance = ______

Describe how the student uses the apparatus in Fig. 5.1 to obtain a range of ammeter and voltmeter readings.

State Ohm’s law.

Using the results in Table 5.1, show that the resistor obeys Ohm’s law.

The student has available an ammeter with five ranges marked:

• $0 - 10\ \text{A}$
• $0 - 200\ \text{mA}$
• $0 - 20\ \text{mA}$
• $0 - 2\ \text{mA}$
• $0 - 0.2\ \text{mA}$

Suggest how the student makes best use of the different ranges during the investigation.

the total resistance of the circuit,

resistance = ______

the reading on the ammeter.

reading = ______

the current in the LDR,

the current in the $1800\ \Omega$ resistor.

The metal wire obeys Ohm's law. State Ohm's law in words.

Calculate the resistance of the metal wire.

resistance = ______

Calculate the resistance of the new wire.

resistance = ______

On Fig. 6.1, draw a line to show how current varies with p.d. for the new wire.

State the range of voltages where the resistance increases.

State why the resistance of the lamp increases as the voltage increases.

State what is meant by an electric current.

Use Fig. 6.1 to determine the current in the filament lamp.

current = ______

Determine the current in the ammeter.

current = ______