Basic Properties of Electric charge notes with video explaination is prepared and uploaded for reference by academic team of expert members of Param Himalaya.
Basic Properties of Electric charge :
1. Charges are of two Types, positive and negative.
2. Like charges repel each other and unlike charges attract each other.
3. Positive and negative charges tends to cancel each other.
4. Additivity of Electric charge :
Electric Charge is additive means total charge on an extended body is the algebraic sum of charges in different regions of the body.
$q= q_{1} + q_{2}+.....q_{n}$
Example : A system has two charges qA = 2.5 × 10-7 C and qB = - 2.5 × 10-7 C , what is the total charge on the system ?
Solution :
Total Charge on the system
q = qA+qB
q = (2.5×10-7 )+ (- 2.5 × 10-7 C) = 0
Hence , the given system is neutral.
5. Conservation of Electric Charge :
According to the law of conservation of Electric charge , net electric charge ( algebraic sum of positive and negative charges ) in an isolated system remains constant.
Charges can neither be created nor be destroyed in an isolated system.
Example :
(i) A glass rod rubbed with a piece of silk cloth get positively charged , whereas the piece of silk cloth becomes negatively charged. The positive charge on glass rod after rubbing is equal to the negative charge on silk cloth. Before rubbing ,
total charge on the system = positive charge on glass rod + negative charge on the silk cloth = zero
in an isolated system. Examples showing the conservation of electric charge:
(i) A glass rod rubbed with a piece of silk cloth gets positively charged, whereas the piece of silk cloth becomes negatively charged. The positive charge on glass rod after rubbing is equal to the negative charge on silk cloth. Before rubbing, total charge on the system (glass rod + silk cloth) = zero.
After rubbing, total charge on the system = positive charge on glass rod + negative charge on the silk cloth = zero.
Hence, electric charge is conserved.
(ii) A neutral particle neutron (charge = 0) in nature is converted into protons and electrons. That is,
$_{0}n^{1}\longrightarrow _{1}H^{1} \text{ (proton)} +_{-1}e^{0} \text{ (electron)}$
Charge before creation of proton and electron = 0
Charge after creation of proton and electron = +e + (-e) = 0
Hence, electric charge is conserved, when a neutron is converted into proton and electron.
(iii) In pair production, $\gamma$-ray photon on interacting with matter transforms into an electron ($e^-$) and positron ($e^+$).
That is
$\gamma \longrightarrow e^- + e^+$
Positron is the anti-particle of electron. Positron has charge, $e = +1.6 \times 10^{-19}$C, whereas electron has charge, $e = -1.6 \times 10^{-19}$C. All other properties of positron are the same as that of an electron.
Charge before interaction = 0 ($\gamma$-ray photon carries no charge)
Charge after interaction = Charge on electron + Charge on Positron = $-e + e = 0$
Hence, electric charge is conserved in pair production.
(iv) During annihilation of matter, an electron ($e^-$) combines with a positron ($e^+$) moving in opposite directions to produce two $\gamma$-ray photons.
$e^- + e^+ \longrightarrow \gamma + \gamma$
Charge before annihilation = $-e + e = 0$
Charge after annihilation = 0 ($\gamma$-ray photon carries no charge)
Hence, electric charge is conserved during annihilation of matter.
6. Quantization of Electric Charge :
Quantized means that it is numberable or integer-countable (like $-2, -1, 0, 1, 2, 3, \dots$ and not $1.2, 1.5, \dots$).
Electric Charge has a grainy nature.As we can count the grains of rice, wheat, etc., similarly we can count the quantization of electric charge. It is a theoretically and experimentally supported property of electric charges. The smallest considered negative and positive charges are those on an electron and a proton, respectively. The charge on a proton is $+e$, and that on an electron is $-e$. Thus, $e$ is an elementary charge.
Value of elementary charge:}
e = 1.602192 \times 10^{-19}C$
According to quantization of charge, any charged body can have charge which is an integral multiple of the basic or elementary charge $e$.
$q = \pm ne$
where
$q$ = total charge,
$n$ = integer ($0, \pm1, \pm2, \pm3, \dots$
$e = 1.6 \times 10^{-19} C$
That is,
$q = 0, \pm e, \pm 2e, \pm 3e, \dots$
Electrons are always transferred in integral values from one object to another object. That is why a charged object can have charge as an integral multiple of the elementary charge $(e)$.
7. Invariance of Electric charge :
Magnitude of charge on a body does not vary , whatever may be the speed of the body . In other words , charge on an object is independent of the speed of the objects.
Charge on a body at rest = Charge on a body in motion
q ( at rest ) = q ( in motion )