Electrostatics is used when paint spraying the panels of a car. The tiny paint droplets are positively charged as they leave the spray gun. The panels of the car are earthed.
Which of the following statements about electrostatic paint spraying is/are correct?
1) Droplets of paint are attracted ...
BMAT SECTION 2 PHYSICS Exam
Questions and Answers (Latest update
2024)
Electrostatics is used when paint spraying the panels of a car.
The tiny paint droplets are positively charged as they leave
the spray gun. The panels of the car are earthed.
Which of the following statements about electrostatic paint
spraying is/are correct?
1) Droplets of paint are attracted to one another.
2) Droplets of paint are attracted to the panels.
3) Droplets of paint can reach parts of the panels that are not
directly in line with the spray gun.
4) The panels of the car body gradually become positively
charged. - Correct Answer ✅All the droplets have the same
(positive) charge so they repel one another. This prevents
them clumping together and leads to a smooth coat of paint
on the car, so statement 1) is incorrect.
As the droplets approach the car, they induce a negative
charge on the surface and this attracts them to it, so
statement 2) is correct.
Droplets that pass behind the car body can be attracted back
to it by induction, so statement 3) is correct.
,BMAT SECTION 2 PHYSICS Exam
Questions and Answers (Latest update
2024)
The car is earthed so, as positive charge is added by the
droplets, electrons flow from earth to neutralise them and the
car body remains neutral. Statement 4) is incorrect.
A charge of 6000 μμC passes through a component in 50
minutes.
What is the average current in the component? - Correct
Answer ✅CURRENT = CHARGE/ TIME
= 6000 *10^-6 / (50*60)
= 6000 *10^-6/ 3000
= 2*10^-6 A
A voltmeter has very .................. resistance, otherwise it
would tend to '............ ............' the component across which
it was connected (because there would be a significant
amount of current in the voltmeter instead of in the
component).
An ammeter has very .................... resistance, otherwise it
would tend to ............... the .................. that it was being
used to measure. - Correct Answer ✅high
,BMAT SECTION 2 PHYSICS Exam
Questions and Answers (Latest update
2024)
short circuit
low
reduce
current
There is a current of 60 mA in a resistor when it is connected
to a 12 V battery.
What is the resistance of the resistor? - Correct Answer
✅RESISTANCE = VOLATGE/CURRENT
= 12 /60*10^-3
= 1 /5*10^-3
= 0.2 *10^ +3
= 2*10 ^ 2 Ω
= 200 Ω
A 72 MΩ resistor is connected across a 1.8 kV power supply.
, BMAT SECTION 2 PHYSICS Exam
Questions and Answers (Latest update
2024)
What is the current in the resistor? - Correct Answer
✅CURRENT = VOLTAGE/ REISTSTANCE
=1.8*10^ *10^6
= 18/ 72*10^4
=1/4*10^4
=0.25*10^-4
=2.5*10^-5 A
OR = 25 μA
In a closed circuit a thermistor is connected to a voltmeter in
parallel and an ammeter in series, with a fixed resistor also
connected in series. What the reading of these two meters
when the temperature of the thermistor decreases? - Correct
Answer ✅As temperature increases the resistance
decreases.
On the ammeter:
the overall resistance of the circuit increases
therefore the current (and the reading on the
ammeter)decreases
On the Voltmeter:
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