[Part 2]- P4- electric circuits 🪫💡

Question 1

In a series circuit, what can we say about the total resistance?

Answer 1

• in a series circuit, resistors in series add together. [Sum/total of resistance].
• This is because the current has to pass through each resistor, in turn and can’t bypass any resistor.

Question 2

In a parallel circuit, what can we say about the total resistance?

Hint: less than the resistance

Answer 2

• in a parallel circuit, the total resistance of the two resistors in parallel is less than the resistance, of the smallest individual resistor.
• This is because with two resistors in parallel, there are two pathways to take- so the total current will flow through the circuit.

Question 3

What are LDR’s [light-dependent-resistors] useful ?

Hint: conditions
Hint #2: detect

Answer 3

• In dark conditions, the LDR [light-dependent resistor] has a high resistance; in the light, the resistance in the LDR is low.
• Therefore LDR’s are useful, since they can be used to detect light.

Question 4

What is a key feature about a thermistor?

Hint: why ?

Answer 4

• the resistance of a thermistor decreases, if the temperature increases.
• when the temperature is low, the resistance of the thermistor is very high; when the temperature is low, the resistance of a thermistor falls to a low level.
• [this is because, increasing the temperature frees more electrons to carry the current, so the resistance of the thermistor decreases]

Question 5

Explain how a thermistor could be used in a incubator for premature babies 👶 🍼

Hint: sensed

Answer 5

• premature babies need to be kept warm, so the incubator will contain a system to detect faults.
• and if the temperature falls, this is sensed by the thermistor, which will then cause a lamp to turn on and an alarm to sound.

Question 6

What are some everyday uses of an LDR ?

Hint: automatic

Answer 6

• automatic night lights
• outdoor lighting
• burglar detectors.

Question 7

Give everyday uses of a thermistor

Hint: engine

Answer 7

• car engine temperature sensors
• electronic thermostats.

Question 8

• Fill in the gaps: In a resistor, when the temperature is low, the resistance of the thermistor is very ____
• ; when the temperature is high, the resistance of a thermistor _____ to a ___ level.

Answer 8

• In a resistor, when the temperature is low, the resistance of the thermistor is very high
• ; when the temperature is high, the resistance of a thermistor falls to a low level.

Question 9

What is the I-V graph for an ohmic conductor ?

Answer 9

Question 10

What is the I-V graph for a filament bulb ?

Answer 10

Question 11

What is the I-V graph for a [semiconductor] diode ?

Answer 11