Advertisements
Advertisements
Question
An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
Solution
The amount of heat (H) produced is given by the joule’s law of heating as H = Vlt
Where,
Current, I = 5 A
Time, t = 30s
Voltage, V = Current × Resistance
= 5 × 20
= 100 V
H = 100 × 5 × 30
= 1.5 × 104 J.
Therefore, the amount of heat developed in the electric iron is 1.5 × 104 J.
APPEARS IN
RELATED QUESTIONS
Why does the cord of an electric heater not glow while the heating element does?
Name any two effects of electric current.
The safety device based on the heating effect of electric current is called a ______.
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal?
Explain why, the current that makes the heater element very hot, only slightly warms the connecting wires leading to the heater.
Derive the expression for the heat produced due to a current 'I' flowing for a time interval 't' through a resistor 'R' having a potential difference 'V' across its ends. With which name is this relation known?
The current passing through an electric kettle has been doubled. The heat produced will become:
(a) half
(b) double
(c) four time
(d) one-fourth
The elements of electrical heating devices are usually made of:
(a) tungsten
(b) bronze
(c) nichrome
(d) argon
Answer the following question.
Write the mathematical expression for Joule's law of heating.
Write scientific reason.
A coil made up of alloy Nichrome is used in the electric heater cooker as a resistor.
Define fuse.
Mark the correct choice
- Assertion: Electric appliances with a metallic body have three wire connections.
- Reason: Three-pin connections reduce the heating of the connecting wires.
An electric iron consumes energy at the rate of 420 W when heating is at the maximum rate and 180 W when heating is at the minimum rate. The applied voltage is 220 V. What is the current in each case?
Your teacher has shown you the following activity.
Activity: The teacher has wound a long insulated piece of wire around an iron nail in the form of a coil. The free ends of the wire are connected to a cell through a switch as shown in Figure 14.3. The current is switched on and some pins are placed near the ends of the nail.
Write down any three questions that come to your mind about this activity
An electric fuse has a body made of ceramic and two points for connecting the fuse wire.
Explain the working of an electric fuse.
______ wire is used in the filament of the bulbs.
A fuse is used in an electric circuit to stop high currents flowing through the circuit.
In the electric equipment producing heat like iron, electric heater, boiler, toaster etc., an alloy such as nichrome is used, not pure metals.
An electric iron of resistance 20 Ω draws a current of 5 A. The heat developed in the iron in 30 seconds is ______.
