Polythene Rubbed with Wool

Q. A polythene piece rubbed with wool is found to have a negative charge of 3 × 10⁻⁷ C. Estimate the number of electrons transferred? expects 2 × 10¹²

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The web of concepts

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Q. A polythene piece rubbed with wool is found to have a negative charge of 3 × 10⁻⁷ C $q = 3 \times 10^{−7}$ C. Estimate the number of electrons transferred?

The playground

Inputs

charge

q

3e-07 C

Outputs

electrons

n

The solution

Solved with ElectricCharge

Given

$q = 3 \times 10^{−7}$ C

Find $n$ .

Working

charge comes in whole electrons(polythene) $q = n \cdot e$
$3 \times 10^{−7} = n \cdot 1.60217663 \times 10^{−19}$
$n = 1.87245272 \times 10^{12}$
$n \approx 2 \times 10^{12}$ to 1 significant figure

Conclusion

Charge comes in whole electrons, so the charge divided by one electron's charge counts the electrons rubbed off the wool onto the polythene.

The Ruby

1require_relative "../physics"23question :polythene_rubbed_with_wool do4  kind :numerical5  describes "A polythene piece rubbed with wool is found to have a negative charge of %{charge}. %{electrons}?"6  given charge: "3e-7 C"7  asks electrons: "Estimate the number of electrons transferred"8end

1require_relative "../questions/polythene_rubbed_with_wool"2require_relative "../science/electric_charges_and_fields/electric_charge"34solve :polythene_rubbed_with_wool, using: ElectricCharge do5  objects :polythene67  take charge: polythene.charge89  electrons = polythene.number_of_charges10  answer electrons:, figures: 11112  conclusion "Charge comes in whole electrons, so the charge divided by one electron's charge counts the " \13             "electrons rubbed off the wool onto the polythene."14end

1require_relative "../solutions/polythene_rubbed_with_wool"23play_with :polythene_rubbed_with_wool do4  title "Polythene Rubbed with Wool"5end

The laws

quantity	written	units	within	from
elementary charge	$e$	C	—	ElectricCharge
charge	$q$	C	—	ElectricCharge
number of charges	$n$	—	—	ElectricCharge
charges a second	$n_{dot}$	s⁻¹	—	ElectricCharge
charging time	$t$	s	0 … 1e+12	ElectricCharge
charge of ground	$q_{g}$	C	—
number of charges of ground	$n_{g}$	—	—
charge of polythene	$q$	C	—
number of charges of polythene	$n$	—	—
charges a second of ground	$n_{dot,g}$	s⁻¹	—
charging time of ground	$t_{g}$	s	0 … 1e+12
charges a second of polythene	$n_{dot}$	s⁻¹	—
charging time of polythene	$t$	s	0 … 1e+12

q_{b} = n_{b} \cdot e

charge comes in whole electrons

n_{b} = n_{dot,b} \cdot t_{b}

charges gathered over a time

q_{g} = n_{g} \cdot e

charge comes in whole electrons(ground)

q = n \cdot e

charge comes in whole electrons(polythene)

n_{g} = n_{dot,g} \cdot t_{g}

charges gathered over a time(ground)

n = n_{dot} \cdot t

charges gathered over a time(polythene)