Transcript electricity revision and electrostatics

Tutorial Questions 1 to 8
Q = It
V = IR
Series
Parallel
I1 = I 2 = I 3
I = I + I2
VT = V1 + V2 + V3
V1 = V2 = V3
RT = R1 + R2 + R3
1 / RT = 1 / R1 + 1 / R2
Short cut if resistors are
identical, divide by the
number of resistors
Expt: For the 4 resistors
1. Measure resistance using an ohmmeter.
2. Find resistance using the colour code. Find tolerance.
For the 33 resistor measure voltage and current then calculate
resistance.
( The maximum current you can use is 0.25 A)
Revision
P = IV
P = V2 ÷ R
P = I2R
E = Pt
Vt
Potential divider
2
1
0V
Tutorial questions 9 to 20
V1 = R1 VT
RT
static
electricity
How is Static Electricity Produced?
An atom will usually have the same number of positives
and negatives
This makes the atom NEUTRAL.
Electron (-)
Proton (+)
Neutron
Charging by
rubbing
TG (HSD)
Electric Field – the space around a charge where electric
forces can be detected.
Field lines show the direction a positive charge would move in.
The closer the lines the stronger the force.
Electrical potential energy, Ew, is the work done in moving a
charge from one point to another.
+
+
+
-
-
Ew = Fd
Electrical potential difference, V, is the work done per unit
charge.
V = Ew÷ Q
Therefore 1 V = 1 J/C
One volt is when one joule of work is done in moving one
coulomb of charge between two points.
-
A
B
-
+
+
+
Remember total energy is conserved.
Work done in moving charge from B to A =
Electrical potential energy at A =
Kinetic energy at B
QV = ½mv2
Tutorial Questions 1 to 8 on page 59
SAQ pages 1 to 8
Purple book Ex 4.7
Gains electrical Ep
In battery chemical potential energy
is changed to electrical energy.
buzzer
Loss of electrical Ep
Bulb changes electrical energy to light and heat.
Resistor changes electrical energy to heat. Heat is dissipated.
Buzzer changes electrical energy to sound.
Electromotive force, emf ( E ) = gain in electrical energy per unit
charge ( in J/C )
Potential difference, pd (V) = loss in electrical energy per unit charge
Read SAQ pages 13 and 16
Tutorial Qu 9 to 13