Electric Circuits

State why the reading on ammeter 2 is also $0.20\ \text{A}$.

Calculate the resistance of T.

resistance = ______ $\Omega$

The temperature of T increases.

Explain why the potential difference (p.d.) across T decreases.

Complete Fig. 6.1 by drawing the circuit symbol for an LDR between points P and Q.

Explain how the voltmeter reading changes as the amount of light falling on the LDR increases.

Show that the current in the $5.0\ \Omega$ resistor is $1.9\ \text{A}$.

Calculate the potential difference (p.d.) between points X and Y.

p.d. = ______

Calculate the total resistance of this arrangement.

resistance = ______

The arrangement is connected to a d.c. power supply.

Voltmeters are placed across the resistors, as shown in Fig. 5.2. There is a current in each resistor.

Compare the readings on the three voltmeters. There is no need for any calculation.

State the relationship between the current $I_B$ in the battery, the current $I_1$ in the fixed resistor and the current $I_2$ in the variable resistor.

State an equation that relates the potential difference (p.d.) $V_B$ across the battery, the p.d. $V_1$ across the fixed resistor and the p.d. $V_2$ across the variable resistor.

The p.d. across the battery is $9.0\text{ V}$. The resistance of R is set at $500\ \Omega$.

Calculate the current in R.

current = ______

the current in the LDR,

current = ______

the reading on the voltmeter.

reading = ______

The brightness of the light on the LDR is gradually increased.

State and explain what happens to the reading on the voltmeter.

Suggest a use for a potential divider made from an LDR and a fixed resistor.

Fig. 7.1 shows a variable potential divider (potentiometer) connected to a $6.0\text{ V}$ battery.

The movable contact can slide between A and B. As it moves, the output voltage changes.

Complete the table below to show the output voltage when the contact is at A and at B.

Explain why the voltage across the thermistor decreases as its temperature rises.

At one temperature, the thermistor has a resistance of $1000\ \Omega$. Calculate the current in the thermistor.

current = ______

the reading on the voltmeter,

reading = ______

the resistance of the thermistor.

resistance = ______

the resistance of the thermistor,

the ammeter reading and to the voltmeter reading.

ammeter reading: ______
voltmeter reading: ______

Determine the resistance of the LDR.

resistance = ______

The intensity of the light incident on the LDR gradually increases.

State and explain how the trace on the oscilloscope screen moves.

the total resistance of the circuit,

resistance = ______

the current measured by the ammeter.

current = ______

The resistance of X is increased.

Explain why the p.d. across the $2.8\text{ }\Omega$ resistor decreases.

A student connects a battery, thermistor X and resistor Y in parallel, as shown in Fig. 5.1.

• The electromotive force (e.m.f.) of the battery is $E$.
• The current in X is $I$.
• The resistance of Y is greater than the resistance of X.

Tick two boxes, one to show the correct statement about the potential difference across Y and the other to show the correct statement about the current in Y.

The potential difference across Y:

is less than $E$ [ ]

is equal to $E$ [ ]

is greater than $E$. [ ]

The current in Y:

is less than $I$ [ ]

is equal to $I$ [ ]

is greater than $I$. [ ]

Calculate the resistance of Y.

resistance = ______

The thermistor is cooled.

Explain why this causes the potential difference across Y to decrease.