Electrical circuits - LDRs and Thermistors

Electrical circuits - LDRs and Thermistors

How do Streetlights come on automatically ?

How can you turn the heating on automatically when it gets cold.

FIrst lets have a look at what you know already about electrical circuits

Multiple Choice

This is the symbol for a...

• Thermistor

• Bulb

• Fixed Resistor

• Ammeter

Multiple Choice

This is the symbol for a...

• Motor

• Ammeter

• Bulb

• Voltmeter

Multiple Choice

This is the symbol for a...

• Fixed Resistor

• Variable Resistor

• Light Dependent Resistor

• Fuse

Multiple Choice

This is the symbol for a...

• Fuse

• Cell

• Fixed Resistor

• Variable Resistor

Multiple Choice

This is the symbol for a...

• Battery

• Thermistor

• Motor

• Fuse

Multiple Choice

This is the symbol for a...

• Light Emitting Diode

• Fuse

• Fixed Resistor

• Variable Resistor

Multiple Choice

What is the best definition for current.

• the flow of charge.

• how much charge flows past a point in a unit of time.

• how much charge there is around the circuit.

• the energy used by charge as it flows.

Multiple Choice

A current of 1.5 A flows for a time and a total of 15 C of charge flows past each point in a circuit. How long does the current flow?

• 22.5 s

• 10 s

• 0.1 s

• 16.5 s

Multiple Choice

What is the relationship between potential difference, current and resistance across a component.

• V = I/R

• I = V x R

• V = R/I

• V = I x R

Multiple Choice

The picture shows an electrical circuit. This circuit is a series circuit because: 

• It has 3 light bulbs.
• The same current flows through all three light bulbs.
• It uses a single battery.
• The electrical current is divided between the three light bulbs.

Multiple Choice

How should an ammeter be connected to measure the current through a bulb?

• In series with the bulb.

• In parallel with the bulb.

• It doesn't matter, you'll always get the same reading.

Multiple Choice

Which type of circuit is better in a situation where you need to control several lights individually with different switches, but they all run off the same power supply?

• Series

• Parallel

• Either.

• Neither.

Fill in the Blanks

What is the unknown current at this wire junction? value and units.

Multiple Choice

State what happens to the total resistance of the circuit and the current through the circuit when switch S is closed.

• The resistance decreases and the current decreases

• The resistance increases and the current increases

• The resistance increases and the current decreases

• The resistance decreases and the current increases

Fill in the Blanks

The ammeter displays a reading of 0.10 A.

Calculate the resistance of the resistor labelled R in ohms. (no units needed)

Fill in the Blanks

The ammeter displays a reading of 0.10 A.Calculate the potential difference across the 45 Ω resistor.

Fill in the Blanks

What is the current through the 75 ohm resistor (V₁)?

Multiple Choice

What is the voltage on the 75 ohm resistor (V₁)?

• 187.5 V

• 120 V

• 93.75 V

• 60 V

Fill in the Blanks

What is the value of the voltage (V1)? (value only needed, no units.

Multiple Choice

Which graph shows the IV graph for a Diode?

Multiple Choice

What will happen to the voltage reading if the temperature on the thermistor increases?

• it increases

• it decreases

• it stays the same

Multiple Choice

The resistance of a light dependent resistor increases when the light intensity decreases

• TRUE

• FALSE

Multiple Choice

Which one is the symbol for 'light dependent resistor'?

Multiple Choice

During night, the output voltage is

• Low

• High

Multiple Choice

When temperature decreases, then the output voltage

• Increases

• Decreases

• Stay the same

Fill in the Blanks

The current in the circuit is 3.5 mA when the potential difference across the thermistor is 4.2 V

Calculate the resistance of the thermistor in ohms. (value only needed).

Multiple Choice

Which one is the symbol for 'light emitting diode'?

Multiple Choice

The resistance of a thermistor increases when its temperature increases

• TRUE

• FALSE