Current and Resistance Chapter 27 Electric Current Flow
- Slides: 11
Current and Resistance Chapter 27
Electric Current Flow of electric charges through a piece of material Amount of flow depends on material and the potential difference across the material Whenever there is a net flow of charge through a region= there is an electric current
Electric Current (I): the rate at which charge flows through a surface Unit of current is ampere= A If ΔQ is the amount of charge that passes though the surface in time (Δt) the average current Iavg= ΔQ/ΔI Electric Current I= d. Q/dt 1 A= 1 C/s
Electric Current The direction of the current is opposite the direction of the flow of electrons Refer to a moving charge as charge carrier If the ends of a conducting wire are connected the electric field is zero within the conductor No net transport of charge Also no current
Resistance Current density (J) units of ampere/meter 2 J=I/A I= nq. Vd. A then J= nq. Vd This above equation is ONLY VALID if current density is UNIFORM and only if the cross-sectional area A is PERPENDICULAR to the direction of the current
Resistance Ohm’s Law For many materials, the ratio of the current density to the electric field is a constant σ that is independent of the electric field producing the current J=σE Further derivations show that R=L/σA which is called resistance
Resistance (R) unit is ohm (Ω) R= ΔV/I 1Ω= 1 V/A circuits use elements called resistors to control the current in the circuit at different places: Two types are: Composition resistor Wire-wound resistor
Resistance Resistivity is the inverse of conductivity ρ=1/σ Unity is Ohm meters (Ω m) Resistance of a uniform material of length(L) R= ρ x L/A If the length of wire is doubled, its resistance doubles If its area is doubled, its resistance decreases by ½
Resistance and Temperature Variation of Resistance with temperature ρ=po[1+α(T-To)] ρ=resistivity at some temp. T (°C) α is the temperature coefficient of resistivity Temperature Coefficient of Resistivity α= (1/ρo)x(Δρ/ΔT) Δρ= ρ - ρo
Superconductors Class of metals and compounds whose resistance decreases to zero when they are below a certain temp. (Tc)
Electrical Power (P) is the rate at which energy is delivered to the resistor by a battery P= IΔV Unit= Watt Power delivered by voltage source to any device P=I 2 R = (ΔV)2/R Unit of power= Watt
- How to find voltage in a parallel circuit
- How resistance opposes the flow of current
- Chapter 21 electric charge and electric field
- Chapter 21 electric charge and electric field
- Electric field k constant
- Dc o/d per item charge
- Constant rate filtration equation
- Force of air resistance
- Chapter 23 electric current circuit happenings
- Conceptual physics chapter 23 electric current
- Chargeflow
- Electric potential and electric field