Currentelectricity Flashcards
When does a body have a positive charge and when does it have a negative charge?
“A body is said to be negatively charged if it has an excess of electrons and positively charged in case of deficit.”
How is the quantity of charge in a body determined?
“The quantity of charge on a body is determined by the number of electrons in deficit ( in case of positive charge ) or the number of electrons in excess (in the case of negative charge.)”
Give the equation for finding the charge on a body. What is the value of charge on an electron?
“When the body has a positive charge Charge Q = ne and Q is positive. When the body has a negative charge Charge Q = ne and Q is negative. The Value of charge on one electron is 1.6 * 10^-19”
Explain: (i) Charge is static in a non-conductor (ii) Flow of charges can occur in a conductor.
“(i) Electrons in non-conductors are tightly bound to their atoms. Excess charge stays localized on the surface. No significant flow of charge within the material. (ii) Electrons in conductors are loosely bound and mobile. Excess charge spreads throughout the volume through electron movement. Electric current flows in conductors due to this charge movement.”
Define current. State its SI unit.
“Current is the rate of flow of charge across the cross section of a conductor. The S.I unit of current is ampere (A).”
What is the relation between current and charge? Give the equation.
“Current flowing across the cross section of a conductor is directly proportional to the amount of charge passing normal to the cross section. Equation: I = Q/t or I = (n*e)/t”
How is current in a circuit measured?
“Current in a circuit is measured by an ammeter by connecting it in series in the circuit. The positive terminal of the ammeter should be towards the positive terminal of the cell. (Or source of current)”
Why is an ammeter connected in series? Why is a voltmeter not connected in series?
“Ammeters have very low resistance to minimize their impact on the circuit’s overall current flow. Placing it in series ensures the measured current remains representative of the entire circuit. Voltmeters have very high resistance to minimize their own current draw and prevent them from altering the voltage they are trying to measure. Connecting it in parallel ensures the voltage across the element remains unaffected.”
What would happen if: (i) An ammeter was connected in parallel instead of series. (ii) A voltmeter was connected in series instead of parallel
“(i) Connecting an ammeter in parallel would divert current giving an inaccurate reading. (ii) Connecting a voltmeter in series would break the main circuit and give no reading.”
Why is current a scalar quantity?
“When two currents meet at a junction their overall effect is simply the algebraic sum of their individual magnitudes like adding or subtracting numbers. This wouldn’t be the case for vector quantities which require considering angles and direction along with magnitude.”
Give the equation for current in the direction of motion of cations in an electrolyte.
“(n1q1 + n2q2)/t Where n1 & n2 = number of cations and anions respectively and q1 & q2 = charge on each cation and anion respectively and t = time taken.”
Define electric potential.
“The potential at a point is defined as the amount of work done per unit charge in bringing a positive test charge from infinity to that point.”
What is a test charge?
“A test charge is a charge of a known small value which is considered such that its presence does not disturb the charges already in that region.”
Explain what is electric potential in 3-4 points.
“The potential at a point in a region of charges is measured in terms of the work done in moving a test charge from a point of zero potential to that point. Since force between two charges is zero at infinite separation we consider potential to be zero when the test charge is at an infinite separation The work done in bringing the test charge from infinity to a point in the region of other charges when divided by the value if the test charge so as to express for unit charge gives us the potential difference at that point.”
When is the potential at the point positive? When is it negative? Explain.
“The potential is positive at a point in the vicinity of a positive charge as work is done by the charge against the repulsive force whereas in the vicinity of a negative charge potential is negative as work is obtained due to the attractive force on the positive test charge.”
State the unit of electric potential.
“The unit of electric potential is volt (V)”
Define potential difference.
“Potential difference between two points is equal to the work done per unit charge in moving a positive test charge from one point to another.”
How is the potential difference in circuit measured? What precaution is taken?
“The potential difference also known as voltage in a circuit is measured using a voltmeter. The positive terminal should be connected to higher potential point.”
When is the potential difference between two points said to be 1 volt?
“The potential difference between two points is said to be one volt if the work done in moving one coulomb charge from one point to the other is 1 joule.”
Define resistance. Why does it occur?
“Resistance = opposition to current flow caused by electron collisions with atoms and each other.”
Give Reason: Electrons do not move in bulk with a continuously increasing speed but there is an overall drift towards the positive terminal.
“Electrons in a conductor exhibit thermal motion bouncing randomly among atoms. When an electric field is applied they experience a force towards the positive terminal. However collisions with atoms constantly disrupt this acceleration preventing a continuously increasing speed. The electrons reach a steady-state ‘drift velocity’ due to the balance between the accelerating force and these collisions. This creates a net movement towards the positive terminal despite the random individual motions.”
Why does the wire heat up? Explain with respect to motion of electrons inside the conductor.
“Essentially the wire heats up because the energy gained by electrons from the electric field gets ‘shared’ with the atoms through collisions increasing their energy (energy of the fixed atoms) and hence the temperature.”
