### Magnetostatics Objectives Part 07

**121 .** If two ends of a circular uniform wire are jointed to the terminals of a battery, the field at the center of the circle **will depend on the radius of the circle**

**122 . ** The iron core within a solenoid has a cross sectional area of 2cm2 and the flux density within the iron is 0.8 Tesla. The total flux is** 0.16mWb**

**123 . ** A flux of 0.6 Wb passes through the air gap of an electric motor. Area of the air gap of the flux density 1 tesla is** 600cm2**

**124 . ** The area of the face of the pole shoe is 1.5cm2 and the total flux is 0.18 mWb. The flux density in the air gap is** 1.2 Tesla**

**125 . ** An aero plane with wing span of 50 meters flies at 540km/h. The component of Earth’s magnetic field perpendicular to the velocity of the plane is 0.2 gauss. The potential difference between tip will be (1 weber/m2 =104 gauss)** 0.15V**

**126 . ** Susceptibility is positive for** Ferromagnetic substances**

**127 . ** The parallel conductors of 10mm diameter each carrying 100 amperes in opposite directions are separated by an air space of 50mm. The conductors are 10m long. The force on each conductor will be in** 0.33N**

**128 . ** A copper disc is rotated rapidly below a freely suspended magnetic needle. The magnetic needle starts rotating with velocity **less than that of the disc and in the same direction**

**129 .** Ferromagnetic substances have **high permeability and susceptibility**

**130 .** Earth’s magnetic field always has a horizontal component except at **the magnetic poles**

**131 .** Diagram Question—

**132 .** A rectangular magnet of magnetic moment M is cut into two places of the same length. The magnetic moment of each place will be **M/2**

**133 . ** The permanent magnets are made of the** ferromagnetic **materials

**134 . ** A permanent magnet** attracts some substances and repels others**

**135 . ** Magnetic moment is a **vector quantity**

**136 . ** The property retentivity of material is useful on the construction of **permanent magnets**

**137 . ** A wire carrying current is bent in the form of a circular loop. Then the magnetic field around each portion of the wire will be** parallel to half portion and perpendicular for the other half.**

**138 .** A solenoid has a flux of 12 mWb and a flux density of 0.9 tesla. The inside diameter if the solenoid must be** 13cm**

**139 . ** Match the followingMaterial/Medium Permeability

i-Free Space** Constant**

ii-Paramagnetic **Slightly more than 1**

iii-Ferromagnetic **100-100,000**

iv-Diamagnetic **Slightly less than 1**

Questions 140 to 142 refer to given data:

It is desired to send a flux of 500microWb across an air gap, 0.1cm long and 25cm2 in cross section, located in a certain magnetic circuit

**140 .** The reluctance of the air gap is **3.19 x 105 ampere turns / weber**