Criado por Christine Laurich
aproximadamente 8 anos atrás
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Questão | Responda |
Current (I) Definition | The rate of flow of electric charge (no. of coulombs flowing past a point in the circuit every second) |
Current (I) Formula | I = ∆Q/∆t |
Direction fo electric current | Always flows from positive to negative, or from big dash to small dash |
e.m.f. Location on diagram | Electromotive force Checks the difference in energy per coulomb between cell |
p.d. Location on diagram | Potential Difference Checks the difference in energy per coulomb between lamp |
e.m.f. Definition | The total energy difference per unit charge around the circuit. (Is potential difference when NO current flows in circuit) |
p.d. Definition | The work done per unit charge to move a small positive charge between two points |
p.d. and e.m.f. in a series circuit | ∑p.d. = e.m.f. across all cells e.g., three lamps of 3V (p.d.), the cell has 9V (e.m.f.) |
p.d. and e.m.f. in a parallel circuit | p.d. = e.m.f. |
Resistance Definition | Measures how difficult it is for current to flow Measured in Ohms (Ω) |
Resistance Formula | Resistance (R) = Voltage (V) / Current (I) |
Resistance proportionalities | R α L R α 1/A R depends on type of material |
Resistivity | R = (ρL)/A Where R = resistance (Ω) ρ = resistivity of the material (Ωm) L = length (m) A = cross sectional area of conductor (m2) |
Diameter in mm to A in m2 | d = 0.1mm --> r = 0.05mm = 5E-5 cross sectional area = πr2 = π(5E-5)2 = 7E-9 m2 |
Ohm's Law | For a metallic conductor at a constant temperature, the current passing α applied p.d. |
Power Definition | Amount of energy used by a device per second (W) |
Power Formula | P = VI |
Power 2nd Formula | P = VI Since V = IR P = I (IR) P = (I2)R |
Energy transformed Definition | Total energy transformed by a lamp is the power (J/s) x time the lamp is on in seconds |
Energy transformed Formula | E = VIt |
Adding resistances Series circuit | R1 + R2 ... Rn = Rtotal |
Adding resistances Parallel circuit | 1/R1 + 1/R2 ... 1/Rn = 1/Rtotal |
Ideal meters Voltmeters | Infinite resistance |
Ideal meters Ammeters | Zero resistance |
Potential Divider Formula | Vout = Vin (R2/R1+R2) |
Assumption of power source having no resistance - true or false? | FALSE Internal resistance |
Internal resistance | p.d. across cell is less than e.m.f. due to energy lost in the internal resistance |
p.d. Formula using internal resistance | V = ε - Ir e.g., find p.d. across cell terminals when e.m.f. = 12, A of internal resistance = 3, internal resistance = 1.5Ω V = 12 - 3x1.5 V = 7.5 V |
Kirchoff's 1st Law | Conservation of charge ∑Amps = 0 by a junction I1 + I2 = I3 + I4 + I5 |
Kirchoff's 2nd Law | ∑e.m.f. = ∑p.d. in a closed loop or ∑V = 0 by a loop E = V1 + V2 + V3 or E - V1 - V2 - V3 = 0 |
Procedure for Kirchoff's Laws | 1) Assume all voltage sources are given. If not, label. 2) Label each branch with a branch current 3) Apply Kirchoff's 1st law at each node, ∑I = 0 4) Apply Kirchoff's 2nd law for each independent loop of the current 5) Solve equation |
Primary cell | Used once, then thrown away Electrochemical reaction is not EASILY reversible |
Primary cell Discharge characteristics | Terminal p.d. loses initial value quickly Stable and constant value for most of it's lifetime Then rapid decrease to zero as the cell discharges completely. |
Secondary cell | Reaction CAN be reversed by running a current INTO the cell |
Secondary cell Advantages | Can charge High uses |
Secondary cell Disadvantages | - Not good for small uses, such as tv remote control or mouse - Lose charge on their own - high "self-discharge", chemical reactions reduce the energy available - this is why primary cells are used more often |
Light Dependent Resistor (LDR) | A device that has a resistance that varies according to the amount of light falling on it's surface High resistance in the dark Low resistance in light |
Thermistor | Resistance decreases with increasing temperature |
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