Components in Series & Parallel Circuits Flashcards

All 24 cards in this deck

In a series circuit, what is true about the current at each point?

It is the same at every point in the circuit.

How is the supply potential difference shared between components in a series circuit?

e.g. two identical lamps on a 3 V supply

The p.d.s across the components add up to the supply p.d.

Each lamp has $1.5$ V across it.

In a parallel circuit, what is the potential difference across each branch?

The same as the potential difference of the supply.

True or false? If a lamp in one branch of a parallel circuit breaks, the components in the other branches stop working.

False. Only that branch stops working; the other branches still get the full supply p.d. and keep working.

What is the total (net) resistance of resistors connected in series?

e.g. a $10\ \Omega$ and a $20\ \Omega$ resistor in series

$R_{total} = R_1 + R_2 + ...$

$= 10 + 20 = 30\ \Omega$

Why is the net resistance of two resistors in parallel less than the resistance of either resistor on its own?

There are more paths for the current, so for the same p.d. the total current is larger, which means a lower total resistance.

How does the overall resistance of a circuit change as more identical resistors are added in parallel?

It decreases, and the relationship is non-linear (it decreases at a decreasing rate).

What are the steps of the core practical to obtain current–potential difference data for a filament lamp?

e.g. a filament lamp on a low-voltage supply

1. Connect the lamp in series with the supply, an ammeter and a variable resistor, with a voltmeter in parallel across the lamp.
2. Adjust the variable resistor and record the current and p.d. at each setting.
3. Plot a graph of current against potential difference.

How is a voltmeter connected to measure the potential difference across a resistor?

In parallel, across the resistor.

How is an ammeter connected to measure the current through a component?

In series with the component.

Why should the circuit be switched off between readings when finding the I–V graph of a fixed resistor?

To stop the resistor heating up, since a temperature rise would increase its resistance.

Describe the current–potential difference graph for a fixed resistor at constant temperature.

A straight line through the origin — current is directly proportional to p.d., so the resistance is constant.

What happens to the resistance of a filament lamp as the current through it increases?

It increases, because the filament gets hotter; the I–V graph curves, becoming less steep.

How does the current through a diode depend on the direction of the potential difference?

Current flows in one direction only; in the reverse direction the resistance is very high and the current is almost zero.

How does the resistance of a light-dependent resistor (LDR) vary with light intensity?

It decreases as the light intensity increases (the resistance is high in the dark).

True or false? The resistance of an NTC thermistor increases as its temperature rises.

False. The resistance of an NTC thermistor decreases as its temperature rises.

A power supply has only fixed whole-number output voltages. Which component can be added, and where, to give a continuously variable potential difference across a lamp?

A variable resistor (rheostat), connected in series with the lamp / power supply.

What are the steps to investigate how the resistance of a thermistor varies with temperature?

e.g. an NTC thermistor in a water bath

1. Connect the thermistor in series with an ammeter and supply, with a voltmeter across it.
2. Put it in a water bath and record current, p.d. and temperature as the water cools.
3. Calculate $R = V/I$ at each temperature and plot resistance against temperature.

Why is a fixed resistor connected in series with a diode when investigating how its current varies with potential difference?

To limit the current, protecting the diode from overheating and being damaged.

True or false? Adding a second identical lamp in series with the first makes each lamp dimmer than the single lamp was.

True. The total resistance is greater, so the current is less and the potential difference is shared between the two lamps.

For lines through the origin on an I–V graph, what does a steeper line show about a component's resistance?

A lower resistance: more current flows for each volt, because resistance equals 1 ÷ gradient.

In a series circuit, which component gets the larger share of the supply potential difference?

The component with the larger resistance.

Why does adding another resistor in series increase the total resistance of a circuit?

The resistors must share the supply p.d., so each has less p.d. across it and the current through the whole circuit falls; less current for the same supply p.d. means more total resistance.

In a parallel circuit, how is the current from the supply related to the currents in the branches?

The supply (total) current equals the sum of the currents in the separate branches.