Electricity Test - 24

Answer is A.

Components connected in parallel are connected so the same voltage is applied to each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.  To find the total resistance of all components, the reciprocals of the resistances of each component is added and the reciprocal of the sum is taken. Hence, the Total resistance will always be less than the value of the smallest resistance. That is, $$\frac { 1 }{ { R }_{ total } } =\frac { 1 }{ { R }_{ 1 } } +\frac { 1 }{ { R }_{ 2 } } ...\frac { 1 }{ { R }_{ n } } ,\quad R={ { R }_{ total } }^{ -1 }$$. 

In this case, the 4 ohms and 2 ohms resistances are connected in parallel. So the total resistance will be $$\frac { 1 }{ 4 } +\frac { 1 }{ 2 }  =\frac { 1 }{ 0.75 } =1.33\quad ohms$$.
As it is a parallel connection, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.  
Total voltage in the circuit is given as V = IR = 1.33 * 3 = 4 V.
Now, the current across the 2 ohms wire is given as I=V/R = 4/2 = 2A.
Hence, 2A of current passes through the 2 ohms wire.

Answer is B.

According to Ohm's law, V = IR. That is, I = V/R.
In this case, the Voltage V = 12 V and Resistance R = 6 ohms.
So, I = 12/6 = 2A.
Hence, the current through the resistor is 2 A.

Answer is D.
In series.
$${ R }_{ total }={ R }_{ 1 }+{ R }_{ 2 }...{ R }_{ n }$$.
In this case, the total resistance is 20+4 = 24 ohms.
The total current in the circuit is calculated from the relation V = IR, that is, I=V/R.
I = 6 V/24 ohms = 0.25 A.
As it is a series connection, the current through each of the components is the same, the voltage across the circuit is the sum of the voltages across each component.
So, the voltage across the radio set is calculated as follows.
The current is 0.25 A and the resistance of the radio set is 20 ohms.
Therefore, V=IR = 0.25 * 20 = 5 V.
Hence, the potential difference across the radio-set is 5 V.

Answer is C.

According to Ohm's law, V = IR. That is, R = V/I.
Here, V = 220 V and I = 5 A.
Therefore, R = 220/5 = 44 ohms.
Hence, the resistance of the heater is 44 ohms. 

Answer is B.

An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field. And those substances have infinite high electrical resistance.
Ideally, the insulation resistance would be infinite, but as no insulators are perfect, leakage currents through the dielectric will ensure that a finite (though high) resistance value is measured.

The above figure shows that the three resistors are connected in parallel to each other.

Electrical current have magnitude and direction but it does not follow law of vector addition. Hence it is a scaler quantity. 

The effective resistance of a circuit containing resistances in parallel is smaller than any of the individual resistances.

Power dissipated by a device that carries current $$I$$ when operated at a potential difference $$V$$ is given by