Chapter 22 Flashcards
what is current?
the motion of charges through a material is called current
What happens when a Capacitor Discharges?
If we connect two plates of a charged capacitor with a metal wire, the charge on each decreases and they eventually become neutral: the capacitor discharges
What are Charge Carriers?
The charge that move in a current called “charge carriers”
Charge Carries are the motion of?
They are the motion of CONDUCTION ELECTRONS, which are free to move around, that forms a current in the metal
What is Random Thermal Motion?
The electron has frequent collisions with ions, but it undergoes no net displacement
What happens if a conductor is placed in an electric field?
The conduction electrons feel a force, they experience a net displacement in the opposite direction of the field
What is Drift Speed?
the drift speed (due to the electric field) is of the order of 10^-4m/s
- The drift speed os MUCH SMALLER than the average speed due to random thermal motion
What is the Speed due to Random Thermal Motion?
The speed due to random thermal motions is of the order 10^8m/s
What is the definition current?
Current is the rate at which charge moves through a wire, The total amount of charge delivered by a steady current (I) during a time interval (Δt) is…
I = Δq/Δt
SI Units = ampere (A) = 1A = 1C/s
What is conventional current?
The flow of positive charge (even though in metals it is the negative conduction of electron that actually flow)
- Electrons move in the direction opposite of conventional current
How are Current and Drift Speed related?
- Charge carriers move in a wire of cross-sectional area A
- The volume of the segment is AΔx
- There are (n) charges carriers per unit volume, each with charge (q)
- The total charge in the segment is the number of carriers times the charge per carrier:
ΔQ = (nAΔΔx)q combined with drift speed…
I = ΔQ/Δt = nAvq
What is the Law of Conservation of Current?
The current is the same at all points in a current-carrying wire
- The current leaving the bulb is exactly the same as the current entering the bulb
What are the two factors that determine current?
- the potential difference
- adding a second battery increase the potential difference, which increase the current - The properties of the wire
- increasing the wires length decreases the current, and increasing its thickness increases the current
What is Ohm’s Law?
In most materials, including most metals, the current is proportional to the potential difference
I = ΔV/R
What is Resistance?
The resistance (R) measures how hard it is to push charges through a wire. the larger the resistance, the harder it is to move charges SI Units = ohms = 1Ω = 1V/A
What is an Ohmic Device?
- The resistance is constant over a wide range of voltages, the relationship between current and voltage is linear, the slope of the I versus ΔV is 1/R
What is a Non-Ohmic?
-The resistance changes with voltage or current, the relationship between current and voltage is nonlinear
What is Resistivity and Resistance?
The resistance of an ohmic conductor is proportional to its length, L, and inversely proportional to its cross-sectional area, A:
R = pL/A
- The resistivity constant of proportionality (p) is called RESISTIVITY of the material
SI Units: Ωm
How are Energy and Power related to each other?
The power supplied by the battery is the rate at which energy is transferred from the battery to the moving charges
P = ΔU/Δt = ΔqΔV/Δt = IΔV
P = E/t
SI Units of Power are Watts (W), 1W = 1J/s
1 kWh is equivalent to what?
1kWh = 3.60*10^6J
Is the amount of energy required to supply 100W of power for 1 hour
What is an Ammeter?
An Ammeter measures current, it is connect in series with the bulb, so that all the charge passing through the bulb also must pass through the meter
What is a Voltmeter?
A Voltmeter measures voltage, it is connect in parallel with the bulb, to measure the potential difference across it
What is a Circuit Diagram?
A circuit diagram is a logical picture of what is connected to what is connected to what
- The actual circuit may look quite different
What is another name for Potential Difference across a battery?
Emf
What is Kirchhoff’s Junction Law?
Junction Law: I1 = I2 + I3
ΣIin = ΣIout
What is Kirchhoff’s Loop Law?
states the sum of the potential differences around any loop formed by the circuit must be zero
ΔVloop = ΣΔVi = 0
What are Resistors in Series?
When resistors are connect in series, the equivalent resistance is always LARGER THAN each individual resistance
Req = R1 + R2 + R3 + …Rn
What are Resistors in Parallel?
When resistors are connected in parallel, the equivalent resistance is always SMALLER THAN each individual resistance
Req = (1/R1 + 1/R2 + 1/R3 +…1/Rn)^-1
What are Capacitor Circuits?
When a capacitor is connect to a battery, charge flows to the capacitor plates, increasing the potential difference
- Once the capacitor is fully charged, there is no further current, the amount of charge on the capacitor is given by…
Q = CΔVc
What are Capacitors in Parallel?
When capacitors are connect in Parallel, the equivalent capacitance is aways LARGER THAN each individual capacitance
Ceq = C1 + C2 + C3 + …Cn
What are Capacitors in Series?
When capacitors are connected in series, the equivalent capacitance is always SMALLER THAN each individual capacitance
Ceq = (1/C1 + 1/C2 + 1/C3 +….1/Cn)^-1
What is another important formula for Potential Difference?
V = U/q or R = V^2/P
