Circuits, Currents & magnets

Circuits, Currents & Magnets

Here is a simple electric circuit. It has a cell, a lamp and a switchRemember an electric current is measured in Amps or Coulombs/Seconds.I = q/t Current = charge / timeAmmeterElectric current (how fast the current is moving) is measured using an ammeter connected in series in the circuit

AHow is AMPs (current) measured?SERIES CIRCUITPARALLEL CIRCUIT current is the same at all points in the circuit.2A2A2A current is shared between the components2A2A1A1AExample problemWhat charge (q) flows in a section of a copper wire in 32seconds if the ammeter measures a current of .8A ?Hint:I = q/t (dont forget units)

Problem #1What charge flows in a cross section of a wire in 10 minutes if the ammeter measures a current of 5mA ?AVoltmeterVoltage (how much power is capable of coming out of this devise of area)The bigger the voltage supplied by the cell, the bigger the current.

VIn a series circuitUnlike an ammeter a voltmeter is connected across the components. Voltage is shared between the components

1.5V1.5V3VAnd In Parallel circuit voltage is the same in all parts of the circuit3V3V3VProblem ASolve the unknown Amps = #1,2? V =#1,2?V1V26V4AA2A1a)Problem BSolve the following Amps #1,2,3? V= #1,2?V1V26V4AA1A2A3b)Resistors in series circuits the equivalent (total)resistance,the total current from the power supply,the current through each resistor,the voltage drop across each resistor, andthe power dissipated in each resistor.

Resistances in series add up

RT = R1+ R2+ R3RT = 20 + 30 + 50 RT = 100 Total current is determined by the voltage of the power supply and the equivalent resistance of the circuit. IT = VT/RT = 125 V/100 = 1.25 AThe voltage drops can be found using Ohm's law. V1 = I1R1 = (1.25 A)(20 ) = 25.0 VV2 = I2R2 = (1.25 A)(30 ) = 37.5 VV3 = I3R3 = (1.25 A)(50 ) = 62.5 VVerify your calculations by adding the voltage drops. On a series circuit they should equal the voltage increase of the power supplyVT= V1+ V2+ V3125 V= 25.0 V+ 37.5 V+ 62.5 V125 V= 125 VWhat is the power for the other 2 resistors?P1 = V1 I1 = (25.0 V)(1.25 A) = 31.250 WResisters in a parallel circuit

Resistances in parallel ; combine according to the sum-of-inverses rule1/RT= 1/R1+ 1/R2+ 1/R31/RT= 1/+ 1/+ 1/20 100 50 1/RT= 5/+ 1/+ 2/= 8/100 100 100 100 RT= 100 /= 12.5 8Total current is determined by the voltage of the power supply and the equivalent resistance of the circuit.IT = VT/RT = 125 V/12.5 = 10 AOn a parallel circuit, each branch experiences the same voltage dropVT = V1 = V2 = V3 = 125 V

The current in each branch can be found using Ohm's law.I1 = V1/R1= (125 V)/(20 )= 6.25 A I2 = V2/R2= (125 V)/(100 )= 1.25 A I3 = V3/R3= (125 V)/(50 )= 2.50 AOn a parallel circuit they should add up to the current from the power supply.IT = I1+ I2+ I310 A= 6.25 A+ 1.25 A+ 2.50 A10 A= 10 A batteries

There are two kinds of batteries: dry cell and wet cell batteries. Here is an example of a dry cellThe zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

Wet cell batteries are most commonly associated with automobile batteriesA wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution.

The earth is like a giant magnet!The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

What is a magnetic domain?Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field. These domains are typically composed of billions of atoms.

How are magnetic fields and electricity connected?When an electric current passes through a wire, a magnetic field is formed.

Electromagnet

When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.