Theme 14 : Introduction To Electric Ciruit

Question 1

State the definition of electric current mentioning a formula (3)

Answer 1

-a flow of charge from one place to another
-charge is carried by electrons moving through a metal wire

Current = charge/ time

Question 2

Explain on batteries (3)

Answer 2

-a battery creates a potential difference between its 2 terminals through chemical reaction
-the 2 terminals are positive and negative
-where negative terminal corresponds to low electric potential and positive corresponds to high electric potential

Question 3

What is the derivation of electron flow (1)

Answer 3

Negative to positive

Question 4

What happens when a switch is open and closed (2)

Answer 4

-an open circuit occurs when the switch is open preventing the flow of electrons
-closed circuit occurs when switch is closed allowing electrons to flow

Question 5

State the definition of emf (3)

Answer 5

-it is the maximum voltage that a better can provide
-when a battery is disconnected from a circuit and carries no current, the pd between its terminal is referred to as EMF
- a real battery can achieve full emf only when the current is zero which is not practical in real life

Question 6

What does the emf of a battery determine and state a formula (2)

Answer 6

-the emf of a battery determines the amount of work it does to move a certain amount of charge around a circuit

Work done = charge x emf

Question 7

What is the relation between current and pd in the battery (1)

Answer 7

-the greater the amount of current flowing through a battery, the greater the reduction in pd between its terminals

Question 8

State and explain the path of an electron in a wire and define drift speed (3)

Answer 8

-electrons move rather slowly through a typical wire
-they experience numerous collisions with atoms in the wire which leads to a path like that
-drift speed is the average speed of electrons

Question 9

State the ohms law and describe the ohmic behavior (3)

Answer 9

V = IR
-materials that exhibit a simple linear relationship between the voltage applied and current
-ohmic materials follow ohms law where the current is directly proportional to applied voltage

Question 10

State the definition of resistivity and state a formula (3)

Answer 10

-it is a property of a material that measures how strongly a material resist the flow of electric current
-greater the resistivity greater the resistance

Resistance = resistivity x length / area

Question 11

What happens to the resistivity if the wire is heated and explain (2)

Answer 11

-increases
-atoms vibrate and collide with electrons

Question 12

What happens to the resistivity in semiconductors if the wire is heated and explain (2)

Answer 12

-decreases
-due to the increases free electrons so current increases

Question 13

State the resistivity in conductors and insulators (2)

Answer 13

Conductors have low resistivity
Insulators have high resistivity

Question 14

What happens to the resistance if area, length and temprature increases (3)

Answer 14

-Resistance decreases as area increases
-resistance increase’s s length increases
-resistance increases as temperature increases

Question 15

What are semiconductors (3)

Answer 15

-they are materials that can conduct electric current with zero electrical resistance
-they are formed when the material is cooled below a critical temperature
-when cooled below critical temperature it can conduct electricity without any energy loss

Question 16

Define critical temperature (1)

Answer 16

-where the resistivity drops to zero at a finite temperature

Question 17

State equations for power (3)

Answer 17

P = IV

P I^2 x R

P = V^2\ R

Question 18

State the conversion from 1 kilowatt hour into joules (1)

Answer 18

3.6 x 10^6

Question 19

How do calculate the total resistance in series and what happens to the current and voltage (3)

Answer 19

R total = R1 + R2 …

-same current flows through all resistors
-voltage is divided across resistors

Question 20

How do calculate the total resistance in parallel and what happens to the current and voltage (3)

Answer 20

1/R total = 1/R1 + 1/R2 ..

-current is the sum of all the currents through individual resistors
-voltage is same through all resistors

Question 21

State Kirchhoffs junction rule: (2)

Answer 21

-at any junction the current entering the junction must equal the current leaving it

I1 - I2 - I3 = 0

Question 22

State the Kirchhoffs loop rule: (1)

Answer 22

-the sum of the pd around a closed loop must be zero