4.2.5 Resistance, 4.2.6 Electrical Workings

Question 1

Describe Resistance and its formula

Answer 1

The current flowing in a circuit can be controlled by adding components with electrical resistance to the circuit. The greater the resistance, the smaller the current that will flow.

R = V/I

Question 2

what is the unit of resistance?

Answer 2

Ohms

Question 3

What is the current voltage characteristic

Answer 3

It is a graph of current plotted against voltage for a resistor.

Question 4

what is the current voltage characteristic of an ohmic resistor?

Answer 4

It is easy to predict the current that will flow through an ohmic resistor because a current is directly proportional to the p.d across it.

Question 5

What is the current voltage characteristic of a filament lamp?

Answer 5

The current is not proportional to voltage.
At first, for low voltages, the graph is straight, showing the current increases at a steady rate as voltage increases. At higher voltages, the graph starts to curve over. The current increases more and more slowly as the voltage is increased.

Question 6

How to determine resistance using a voltmeter and ammeter?

Answer 6

• Set up the circuit according to the image displayed.
• Set the output of the power supply to 2V.
• Measure and record the p.d across the resistor and the current through it.
• Calculate the resistance of the resistor.
• Repeat the process with other resistors
• Connect the lamp in place of the resistor. Set the supply so that the p.d. across the lamp is 2.0 V. Measure the current and calculate the resistance.
• Repeat for several different p.d.s (making sure that you do not exceed the maximum operating voltage of the lamp). How does the resistance of the lamp change as it gets brighter?

Question 7

What are the factors affecting the resistance of a wire (conductor)?

Answer 7

1. Length: ↑L ↑R
2. Diameter: ↑D ↓R
3. Temperature: ↑T ↑R
4. Type of material: better conductor = lower resistance

Question 8

State the formula for Quantity of resistance and the relations to each variable

Answer 8

Resistance is proportional to length
Resistance is inversely proportional to Diameter / Cross sectional Area
P = (R x A) / l
P : Quantity of Resistance
R : Resistance
A : area
l : length

Question 8

What is Ohms law?

Answer 8

Ohms law states that the voltage across a resistor is directly proportional to the current through it. This is only true if the temperature of the resistor or the lamp remains constant.

Question 9

Describe the transfer of electrical energy

Answer 9

Electrical energy is transferred from the battery or power source to the circuit components then into surroundings by electric circuits.

Question 10

What is the formula for electrical power?

Answer 10

FORMULA: P = IV

Electrical power = Current x Potential difference

Question 11

What is the formula for electrical energy transformed?

Answer 11

FORMULA: E = IVt

Electrical energy transformed = Voltage x Current x time

Question 12

What is the formula for one watt?

Answer 12

FORMULA: 1W = 1J/s

1 Watt = one joule per second